Stephen Kastenberg

Stephen J. Kastenberg


Stephen J. Kastenberg focuses on complex business litigation with an emphasis on antitrust and competition, securities, and corporate governance litigation. He has successfully defended public and private companies and universities in federal and state lawsuits, including class actions, throughout the United States. He also regularly represents clients as plaintiffs in business disputes, or assists them through internal investigations. Stephen is based in Philadelphia and is a member of the firm’s Elected Board and Senior Leadership Team.

In his nearly 30 years of litigation experience, Stephen has achieved a significant number of victories through trial, arbitration, summary judgment, advantageous settlement, and on appeal. His clients range from Fortune 100 multinational corporations to privately held companies and nonprofit organizations, and span such industry sectors as pharmaceuticals, chemicals, investments, media and technology, real estate, financial services, and higher education.


Representative Matters

  • Nasdaq, Inc. v. Exchange Traded Managers Group et al.: lead counsel in securities contract dispute that resulted in judgment in favor of client of more than $80 million. See Nasdaq, Inc. v. Exchange Traded Managers Group et al., No. 17 civ. 8252, 2019 U.S. Dist. Lexis 220135 (S.D.N.Y. Dec. 20, 2019)
  • Served as lead counsel for NASDAQ OMX Group in numerous claims and regulatory matters arising from the commencement of trading of stock during the Facebook IPO; obtained an injunction against an exchange member seeking to assert substantial claims in arbitration against NASDAQ.
  • Served recently as lead counsel in defending a global pharmaceutical company in two unrelated 10-figure civil antitrust cases class actions asserting claims for monopolization and collusive dealing. In one matter, obtained summary judgment, affirmed on appeal, and decertification of an indirect purchaser class. In the second, resolved the case on terms favorable to the client after reducing the indirect purchase class from 50 states to four.

Professional Highlights

Judicial Clerkships

Hon. Bailey Aldrich, U.S. Court of Appeals for the First Circuit, 1992-1993

Professional Activities

American Bar Association, Antitrust Section

New Jersey State Bar Association

Pennsylvania Bar Association

Philadelphia Bar Association

Ballard Spahr's Pro Bono Committee

Recognition & Accomplishments

The Legal 500 US, Antitrust - Civil litigation/class action - defense, 2019-2024; Antitrust - Civil litigation/class action - plaintiff, 2019, 2020

Chambers USA, antitrust, litigation: general commercial law (Pennsylvania), 2007-2024

The Best Lawyers in America, commercial litigation, securities litigation, 2012-2024; "Lawyer of the Year," Litigation - Securities (Philadelphia), 2020

Speaking Engagements

"Ascertaining Ascertainability," HarrisMartin's Antitrust Pay-for-Delay Litigation Conference, Philadelphia, PA, September 10, 2015

Faculty, HarrisMartin's Antitrust Pay-for-Delay Litigation CLE Conference, Philadelphia, September 22, 2014

Board Memberships & Community Service

New Jersey Scholars Program, Member and past President

Lawyers' Committee for Civil Rights, Director and Trustee

Police Corruption Task Force, past appointee by Philadelphia Mayor Edward Rendell


Co-author, "NCAA Scores Key Victory in Case Involving Paying Student Athletes," Philadelphia Business Journal, October 5, 2015 

Co-author, "The Corporate Antitrust Policy—Privileged or Not?" Law360, November 7, 2014

Co-author, "Landmark Lawsuit Shapes NCAA and the Future of Student-Athlete Compensation," Philadelphia Business Journal, August 19, 2014



Harvard Law School (J.D., cum laude, 1992)
Managing Editor, Harvard Journal on Legislation

Princeton University (A.B., cum laude, 1988)


New Jersey


Supreme Court of New Jersey

Supreme Court of Pennsylvania

U.S. District Court for the Eastern District of Pennsylvania

U.S. Court of Appeals for the Second Circuit 

U.S. Court of Appeals for the Third Circuit

U.S. Court of Appeals for the Fourth Circuit

U.S. Court of Appeals for the Ninth Circuit

U.S. Court of Appeals for the Tenth Circuit

U.S. Court of Appeals for the Eleventh Circuit