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Stuart H. Sostmann

Portrait of Stuart H. Sostmann

With over two decades of experience as a litigator, Stuart concentrates his practice in the area of commercial general liability. He routinely handles high exposure matters in the fields of product liability, premises liability, auto liability, construction litigation, marine liability, dram shop and commercial litigation. This includes cases involving personal injuries and property damage claims.

As the Managing Attorney of the firm's third-largest office, Stuart oversees the daily operations, including the supervision of 75 employees. In addition to his managerial duties, Stuart serves as the Casualty Supervisor, where he ensures that all client matters are handled promptly, professionally, and effectively by the team of attorneys.

In his career, Stuart has represented manufacturers, suppliers and retailers in product liability matters, including electronics, medical equipment, food products, appliances, farm equipment, plumbing equipment, power tools, toys and sports and recreational equipment. He frequently represents property owners, retailers, pharmacies, general contractors, subcontractors and utilities in premises liability litigation. He has tried numerous cases to verdict in counties throughout Western Pennsylvania.

A significant portion of Stuart’s practice has been devoted to construction litigation. These cases are highly complex and require deep industry knowledge and experience. Stuart has handled a wide range of construction injury and defect cases, representing contractors, subcontractors, material suppliers, engineers, architects, and other construction professionals throughout Pennsylvania. His experience includes defending against claims involving construction defects such as water intrusion from faulty roofing or window and door seals, cracked foundations or improper waterproofing, structural and design issues, mold intrusion, drywall defects, and soil subsidence, heaving, or movement.

Stuart attended the University of Pittsburgh graduating with a B.A. in Political Science. He then attended the University of Pittsburgh School of Law where he participated in the Appellate Moot Court Program, Student Bar Association and the Health Law Certificate Program. He obtained his juris doctor from the University of Pittsburgh School of Law.

Stuart currently serves on the Marshall Dennehey Diversity, Equity and Inclusion Committee working to improve the recruitment, retention and advancement of diverse attorneys and professionals. He is the former President of the Pennsylvania Defense Institute, an organization of civil defense attorneys, executives of insurance companies and self-insured corporations. Stuart is also a member of the Allegheny County Bar Association and the Academy of Trial Lawyers of Allegheny County. Among his many honors, he is Rated AV® Preeminent™ by LexisNexis Martindale-Hubbell and is recognized among the Best Lawyers in America for his work in product liability litigation. Stuart is additionally recognized as Pennsylvania Super Lawyer.

    • University of Pittsburgh School of Law (J.D., 1999)
    • University of Pittsburgh (B.A., cum laude, 1996)
    • Pennsylvania, 1999
    • Supreme Court of the United States, 2023
    • AV® Preeminent™ by Martindale-Hubbell®
    • The Best Lawyers in America®, "Lawyer of the Year," Pittsburgh, Product Liability Litigation – Defendants (2026)
    • The Best Lawyers in America®, Product Liability Litigation - Defendants (2022-2026)
    • Pennsylvania Super Lawyers (2018-2022; 2025-2026)
    • Allegheny County Bar Association
    • American Bar Association
    • Pennsylvania Defense Institute, President 2022-2023; Executive VP of Operations 2021-2022; Executive VP of Programming 2020-2021
    • AI in the Legal Profession, Marshall Dennehey Client Presentation, September 2024
    • Civil Litigation State of Affairs – The Impact of COVID-19 in Pennsylvania and New Jersey & What’s Next, Marshall Dennehey Client Webinar, May, 2021
    • An Overview of Construction Defect Litigation in Pennsylvania, Nationwide Insurance Company, December 16, 2014
    • Commercial Defense Practice in New York, New Jersey & Pennsylvania, Nationwide Insurance Company, December 5, 2014
    • Brief Overview of Pennsylvania Contractual Indemnity and Additional Insured Issues, Nationwide Insurance Company, April 2012
    • Discoverability and Proper Use of Claim Notes, Berkley Mid-Atlantic, October 2011
    • “Yes! Waivers of Liability for Recreational Activities Are Still Effective in Pennsylvania,” Defense Digest, Vol. 23, No. 1, March 2017
    • "Timing Is Everything, Even for Bad Faith Claims," Defense Digest, Vol. 6, No. 1, February 2000 
    • Obtained a defense verdict following a three-day jury trial in a slip and fall injury case. The plaintiff slipped in the lobby of a commercial building and claimed a serious and ongoing injury to her right shoulder.  Plaintiff alleged she fell due to a wet floor caused by the facilities management’s cleaning process and the lack of sufficient visible wet floor caution signs. Plaintiff underwent two surgeries, claimed ongoing pain and suffering, and sought $500,000 prior to trial. We represented the building ownership and the facilities management company. Problematic for the defense was the lack of a surveillance video of the incident, photographs of the lobby contemporaneous to the incident, or an incident report.  Despite this, we persuaded the jury to find for the Defense by establishing a consistent and credible history of habitual practice in the placement of wet floor signs across the lobby in highly visible areas. We also won the credibility battle through our well-prepared witnesses.  Although faced with a sympathetic plaintiff with a substantiated history of medical treatment, we succeeded by presenting the case using “old school” personal injury defense tactics that were necessary due to the lack of video, photographs, and documentation.    
    • Successfully argued a precedent-setting case in the Pennsylvania Superior Court where a waiver of subrogation clause in a construction contract was applied to building damages caused by a windstorm three years after the project was completed. 
    • Successfully defended a product installer at trial in a single vehicle accident, where the placement of the product in the vehicle was claimed to be the cause of the crash at high speed.  A defense verdict was obtained after a 5 day jury trial where the demand was $800,000 prior to trial.

Results

Defense Verdict Following Jury Trial in Slip and Fall Case in the Court of Common Pleas of Allegheny County.

The plaintiff slipped in the lobby of a commercial building and claimed a serious and ongoing injury to her right shoulder. She alleged she fell due to a wet floor caused by the facilities management’s cleaning process and the lack of sufficient visible wet floor caution signs. The plaintiff underwent two surgeries, claimed ongoing pain and suffering, and sought $500,000 prior to trial.  We represented the building ownership and the facilities management company. Problematic for the defense was the lack of a surveillance video of the incident, photographs of the lobby contemporaneous to the incident, or an incident report. Despite this, we persuaded the jury to find for the defense by establishing a consistent and credible history of habitual practice in the placement of wet floor signs in highly visible areas across the lobby.  We also won the credibility battle through our well-prepared witnesses. Although faced with a sympathetic plaintiff with a substantiated history of medical treatment, our attorneys succeeded by presenting the case using “old school” personal injury defense tactics that were necessary due to the lack of video, photographs, and documentation. 

Defense Verdict Secured in Slip-and-Fall Jury Trial

We obtained a defense verdict following a three-day jury trial in a slip-and-fall injury case in the Court of Common Pleas of Allegheny County. The plaintiff slipped in the allegedly wet lobby of a commercial building and claimed a serious and ongoing injury to her right shoulder. Problematic for our case was the lack of a surveillance video of the incident, photographs of the lobby contemporaneous to the incident, or an incident report. Despite this, we persuaded the jury to find for the defense by establishing a consistent and credible history of habitual practice in the placement of wet floor signs across the lobby in highly visible areas. 

Thought Leadership

How I Made Office Managing Attorney: 'Stay True to Yourself, and Things Will Work Out to Your Benefit,' Says Stuart Sostmann of Marshall Dennehey

January 3, 2025

"When I was a younger attorney, I displayed arrogance at times to cover up various insecurities. My advice would be to stay true to yourself, and things will work out to your benefit."

Defense Digest

On the Pulse…Construction Injury Litigation Practice Group

December 1, 2023

Recent data released from the United States Bureau of Labor Statistics reveals that construction laborers accounted for 11.9% of all reported fatal falls, slips, or trips in 2020 across all occupations. Sixty percent of all construction laborers perform their work near or around moving mechanical parts or in close proximity to large moving objects. Fifty percent of these workers reportedly make use of PPE. Construction sites are among the most dangerous places to work in the United States. Indeed, in 2020 alone, construction laborers accounted for 8.9% of all workplace deaths due to exposure to harmful substances or environments. With millions of accidents reported each year, injuries to construction workers are often serious or even catastrophic.  This type of litigation is fraught with difficulty since it tends to involve sophisticated legal issues, multiple parties, multiple causes of action, complex relationships, and problematic factual situations. The law in this area continues to evolve as existing rules and precedent are continually challenged, overturned, replaced, or modified.  Marshall Dennehey’s Construction Injury Litigation Practice Group understands these complex relationships and issues. Our firm has a significant presence in the construction industry in the representation of construction companies/prime contractors, commercial property owners/ managers, developers, design professionals, and demolition, electrical, roofing, and various other trade subcontractors in a wide array of serious loss cases where there is often catastrophic injury or death. With decades of experience, our diverse team of attorneys regularly defends our clients in a multitude of personal injury matters arising out of the construction process. We handle everything from catastrophic injury or death due to contact with objects or equipment, fatal or catastrophic transportation incidents, roofing incidents, and scaffolding/ladder incidents, to the more routine worksite slip and fall incidents.  Our defense approach is aimed at the early identification of key issues and is predicated on developing the earliest possible defense strategies tailored to the individual case and client. Our involvement often begins with pre-litigation accident investigation, claims analysis, best practices related to client document and evidence retention, and early assessment of risk/liability transfer opportunities to shift liability and exposure under the terms of a construction contract, including indemnification and additional insured coverage issues. Our diverse team of trial attorneys have significant experience in handling some of the most high-profile and complex construction litigation matters taking place across the United States, and we have proven time and again, that we are ready and able to try even the most challenging construction injury matters to verdict with the skills needed to prevail.  The depth of our experience is the key to our legal defense in construction injury matters. Our professionals have considerable breadth of experience in this domain. They understand the evolving and complex laws surrounding this volatile area of practice, including issues relating to insurance coverage and claims disputes, additional insured coverage, product liability, workers’ compensation, the statutory employer doctrine, contractor licensing issues, Occupational Safety and Health Act (OSHA) compliance and workplace safety issues, and the peculiar risk doctrine. Through the use of cutting-edge technology and aggressive claim investigation, we are able to assess liability exposure and potential damages issues early on in a case so, together with the client and insurer, we can effectively resolve the case. Our unique strategy and team approach consists of experienced partners, associates, and paralegals capable of handling the basic, as well as the highly-sophisticated and complex, construction injury litigation matters throughout Pennsylvania, New Jersey, Delaware, Ohio, Florida, New York, and Connecticut.  We look forward to your inquiries and remain at your disposal for presentations or seminars your company may desire.     Defense Digest, Vol. 29, No. 4, December 2023, is prepared by Marshall Dennehey to provide information on recent legal developments of interest to our readers. This publication is not intended to provide legal advice for a specific situation or to create an attorney-client relationship. ATTORNEY ADVERTISING pursuant to New York RPC 7.1. © 2023 Marshall Dennehey. All Rights Reserved. This article may not be reprinted without the express written permission of our firm. For reprints, contact tamontemuro@mdwcg.com. 

Firm Highlights

Thought Leadership

New Jersey Appellate Division Affirms Exclusion of Legal Malpractice Expert as Impermissible Net Opinion

Jack Slimm and Jeremy Zacharias obtained a favorable decision on behalf of their client in a case centering on the admissibility of expert testimony in legal malpractice actions. In Martin v. Loury, the New Jersey Appellate Division affirmed the exclusion of a plaintiff's legal malpractice expert, holding that the expert's opinions on causation and damages were too speculative to support the malpractice claim. The legal malpractice action arose from an underlying employment dispute involving claims for damages stemming from the breach of an employment agreement. The plaintiff alleged that defense counsel committed malpractice during a second trial by failing to recall the plaintiff as a rebuttal witness after the employer's CEO testified. According to the plaintiff's expert, additional rebuttal testimony would have bolstered the plaintiff's damages claims and led to a more favorable result. Both the trial court and the Appellate Division rejected that theory. The courts found that the expert could not explain how the proposed rebuttal testimony would have altered the outcome of the underlying case or resulted in any additional recoverable damages. Notably, the trial judge in the underlying employment matter had already rejected the CEO's testimony as not credible and had accepted the damages analysis advanced by the plaintiff. The court had also determined that the amount of damages was not genuinely disputed. As a result, the expert's opinion that additional rebuttal testimony would have produced a better outcome was unsupported by the record and based on speculation rather than evidence. The Appellate Division agreed that neither the plaintiff nor the expert could identify any actual damages attributable to the alleged malpractice or demonstrate the required element of proximate causation. The court further upheld the trial court's application of New Jersey's net opinion doctrine, finding that the expert failed to provide the necessary "why and wherefore" supporting his conclusion that the attorney's conduct caused a compensable loss. Because the opinions rested on unquantified possibilities rather than demonstrable facts, they were inadmissible. Key Takeaway for Legal Malpractice Defendants For attorneys and firms defending legal malpractice claims, Martin v. Loury underscores the importance of closely scrutinizing an opponent's expert report on the critical elements of proximate causation and damages. The decision demonstrates that a malpractice claim cannot survive where an expert merely speculates that different litigation tactics might have produced a better result. Instead, the plaintiff must present admissible expert testimony grounded in the record that explains how the alleged attorney error probably changed the outcome of the underlying matter and resulted in measurable damages.

Thought Leadership

Supreme Court of Pennsylvania Holds That Public Policy Does Not Prevent Insurance Coverage for Sex Trafficking Claims

On July 21, 2026, the Supreme Court of Pennsylvania issued an opinion emphasizing the limited circumstances in which courts may invoke public policy to bar insurance coverage, holding in Samsung Fire & Marine Insurance Co., Ltd. (U.S. Branch) v. RI Settlement Trust that Pennsylvania public policy does not preclude coverage for claims alleging that insureds enabled or profited from human sex trafficking. The decision rejects a line of federal district court decisions predicting otherwise and reinforces that Pennsylvania courts will invoke the public policy doctrine only in the clearest of circumstances. RI Settlement is particularly significant because it arose on certified questions from the United States Court of Appeals for the Third Circuit, giving the Supreme Court the opportunity to resolve an issue on which federal courts had predicted Pennsylvania law differently. RI Settlement arose out of four separate civil complaints in which the underlying plaintiffs alleged that, as minors, they were the victims of human sex trafficking at various hotels in Philadelphia. The plaintiffs claimed that the hotel owners were negligent in failing to stop the sex trafficking from happening at their hotels. After the filing of the lawsuits, the hotel owners sought coverage under their Commercial General Liability policies. The insurers initially defended the hotels under Reservation of Rights letters, though the carriers later filed Declaratory Judgment actions seeking declarations that they did not owe a duty to defend or indemnify. In short, the insurers argued in the alternative that they did not owe any obligation to provide coverage based upon Pennsylvania public policy (because the claims violated the Human Trafficking Law – 18 Pa.C.S. § 3011) and the terms and conditions of the policy. On motions for judgment on the pleadings, the District Court found for the insurers on the basis of public policy: There is no duty to defend or indemnify against actions arising out of an insured's criminal conduct related to the sex trafficking of minors. The Court appreciates that it may make public policy the basis of a judicial decision only in “the clearest of cases.” See Minnesota Fire & Cas. Co. v. Greenfield, 589 A.2d 854, 868 (Pa. 2004) (quoting Hall v. Amica Mut. Ins. Co., 648 A.2d 755, 760 (Pa. 1994)). Yet, the Court strains to imagine a clearer case than the one presented here in which the facts alleged indicate that Policyholders engaged in criminal conduct in violation of Pennsylvania's Human Trafficking Law. The hotel owners appealed the matter to the Third Circuit, which petitioned the Supreme Court of Pennsylvania to grant review of two certified questions of law: (1) whether Pennsylvania law had an “overriding public policy” against sex trafficking, such that an insurer’s duty to defend and/or indemnify is abrogated when an insured is alleged to have enabled or profited from such trafficking; and (2) if yes, is that duty abrogated whenever the insured’s alleged conduct would constitute a violation of the Pennsylvania Human Trafficking statute. Importantly, the certified questions did not ask the Supreme Court to determine whether the policies afforded coverage under their terms. Rather, the court was asked only whether Pennsylvania public policy independently barred coverage. As a result, the court assumed for purposes of answering the certified questions that the insurers otherwise owed a duty to defend and addressed only the public policy issue, leaving all policy-based coverage defenses for further proceedings. Because the court concluded that the answer to the first certified question was “no”, it did not reach the second issue. In reaching its determination that Pennsylvania public policy does not prohibit insurance coverage for sex trafficking claims, the court limited the impact of its decision in Minnesota Fire & Cas. Co. v. Greenfield, 855 A. 2d 854, 855 (Pa. 2004), which the RI Settlement opinion emphasized as having been an “Opinion Announcing Judgment of the Court” – or a plurality opinion. In Greenfield, the insured homeowner was sued by the estate of his houseguest who overdosed from heroin that he sold to her. The matter wound its way to the Supreme Court, which determined that the insurer did not owe a duty to defend or indemnify based upon Pennsylvania public policy, which criminalized the sale and use of heroin as a Schedule I narcotic. In RI Settlement, the court “decline[d] the invitation” to extend the rationale of the three-justice plurality in Greenfield beyond cases involving Schedule I controlled substances. In so holding, the justices in RI Settlement refused to “divine an overriding public policy pronouncement by the General Assembly by virtue of its enactment of the Human Trafficking Law.” The opinion further states that it is not “within the purview of this Court to rank the magnitude of the public policy underlying the various crimes defined in the Crimes Code. It is sufficient for the work of the courts to know that the General Assembly has identified conduct it deems harmful and dangerous to the maintenance of an orderly society and criminalized it.” While the court declined to declare that Pennsylvania public policy prohibits coverage for sex trafficking claims, the opinion in RI Settlement expressly states that insurers are free to include appropriate exclusionary language for such causes of actions in their policies if they desire to do so. It will certainly be interesting to see whether the insurance industry accepts the court’s invitation, or perhaps whether the Pennsylvania legislature steps in to clarify that sex trafficking claims are indeed of the type or magnitude that they should not be covered by insurance. In any event, we will, of course, continue to monitor this and other insurance coverage issues that arise before courts in Pennsylvania, New Jersey and throughout our firm’s geographic footprint and around the country.

Thought Leadership

Court Allows Recklessness and Punitive Damages Claims to Proceed After Work‑Zone Crash

In a case where a defendant filed preliminary objections against allegations of recklessness and punitive damages, the Susquehanna County Court of Common Pleas denied these preliminary objections. This case stems from a motor vehicle accident, where the defendants car struck the plaintiffs car after the defendant allegedly fell asleep at the wheel, going at a high rate of speed, through a construction work zone. Defendant first objected to the general allegations throughout the plaintiff’s complaint pertaining to “reckless” conduct contending that there were insufficient factual allegations to support the claim of reckless conduct. Defendant next objected to the plaintiffs claim for punitive damages, as punitive damages may only be assessed against a motorist for falling asleep while driving if there is further evidence to prove driver was aware of their drowsiness and risk of falling asleep. Lastly, defendant objected to plaintiffs complaint, claiming it lacked specificity. The court here found that the plaintiff had included in the complaint specific allegations related to the defendant’s alleged recklessness, including allegations regarding speeding in a work zone, almost striking the flagger, falling asleep at the wheel, and striking the plaintiffs vehicle which was stopped. Additionally, the court noted that falling asleep does not come without warning. The court found that these allegations were sufficient to support an allegation of recklessness at the pleadings stage.

Result

No-Cause Jury Verdict Secured in Wrongful Death Trial

We successfully obtained a no-cause jury verdict in a 13-day wrongful death trial. The decedent, a 59-year-old man, was admitted to the emergency room on February 15, 2019, with complaints of abdominal pain, decreased appetite, and constipation, despite the use of laxatives. The patient did not complain of any nausea, vomiting, or diarrhea. He had a significant medical history including diabetes, hypertension, prior coronary artery stenting, morbid obesity (with past gastric bypass surgery), longstanding ventral hernia, and back pain. A CT scan revealed multiple hernias and a potential closed-loop bowel obstruction, leading to a surgery consultation. Our client, an emergency general surgeon, interpreted that the patient did not have a closed loop or any significant obstruction and recommended non-surgical management. The patient was approved to have clear liquids, and had a vomiting incident shortly after, but our client was not notified. The patient was returned to NPO status, and after improving overnight, he was returned to “clears” and additional medical and renal consults were ordered. Our client did not receive any communications from the residents/nurses of any changes in the patient’s condition. On February 18, 2019, two rapid responses were called due to increased heart rate and vomiting. It is believed that the vomiting resulted in aspiration, causing sepsis, ultimately leading to the patient’s death. During the trial, the plaintiff’s sole medical expert highlighted imaging on the wrong hernia, which called into question all of his opinions in the case. We made key objections related to the expert testimony, limiting what the allegations were, and preventing new allegations from being made. After approximately two and a half hours of deliberating, the jury returned a no-cause verdict.