But SummerSlam is serious business. One of WWE’s most popular pay-per-view matches, it is the seventh-most expensive event held at the Barclays Center since it opened in September 2012. With an average ticket resale price of $332, SummerSlam cost more to attend than concerts by Beyoncé, Pearl Jam or Jay-Z, according to the website SeatGeek.

Mr. Stewart, a wrestling fan whose tense relationship with the wrestler Seth Rollins has been well-documented, surprised spectators Sunday by stepping into the ring.

Slipping under the ropes during a winner-takes-all match between Mr. Rollins and John Cena for the World Heavyweight and United States champion titles, Mr. Stewart threw a metal chair into Mr. Cena.