A shirtless fan trend known as "Tarps Off" that began at Busch Stadium in St. Louis last Friday has spread to Major League Baseball stadiums in Detroit, Tampa Bay, Philadelphia, Seattle and Anaheim, California. The trend involves fans gathering in a stadium section, removing their shirts and twirling them above their heads.

The phenomenon started when the St. Louis Cardinals offered tickets to a club baseball team affiliated with Stephen F. Austin State University, which was in Alton, Illinois, for the National Club Baseball Division II World Series. Seventeen players attended, and dozens of others joined the initial group. A couple hundred fans created a ruckus in right field as the Cardinals beat the Kansas City Royals 5-4 in 11 innings.

Cardinals manager Oliver Marmol bought tickets for the shirtless revelers for Saturday's game, and they returned. The Cardinals' mascot Fredbird joined the shirtless celebration.

"It's hard not to have fun when the fans are like that. We've got the best fans in the world, but it seems like the younger generation makes it more like a college atmosphere," Cardinals shortstop Masyn Winn said.

More shirtless fans cheered for the Cardinals in Tuesday's game against the Pirates, when Ivan Herrera hit a three-run homer to lift the Cardinals to a 9-6 win in 10 innings. A similar outbreak of shirtless fans broke out at a Tampa Bay Rays game on Monday and again Tuesday. A small group of fans celebrated shirtless in Philadelphia as the Reds and Phillies played in the rain.

Chad Bitzer, one of the participants, said, "Cause everyone else was taking it off. Why not?" He also said, "Great Northwest night. We live for the summers. We live for the good weather."

At Angel Stadium, fans waved shirts above their heads and chanted "Sell the team!" during the Angels' 2-1 walkoff victory over the Oakland Athletics. Attendance for the Angels has fallen 20 percent over the past 20 years. Since 2010, the Angels have made the postseason just once and have failed to build a consistent contender despite carrying payrolls near the top half of baseball for much of Arte Moreno's tenure. Moreno explored selling the team following the 2022 season and backed away from the process in early 2024, citing "unfinished business" in a podcast interview.

Attendance is up at big-league stadiums this season, averaging roughly 1,000 more fans per game than a year ago through Monday's contests. If the trend continues, baseball could average 30,000 fans per game for the first time since 2016.