Major League Baseball is experiencing an epidemic of (mostly) guys being dudes.

At ballparks all across the country, groups consisting of mostly young men are joining in on the “Tarps Off” trend that’s loud, goofy, infectious and new to the baseball world. Joining in on the fun is simple: Go to the section where the party is happening, take off your shirt and start twirling it above your head.

Soccer-like chants or singing usually follow — injecting a jolt of energy for a sport that is occasionally chided for its lack of energy inside the stadium.

After getting it’s start in St. Louis last Friday, it has spread across the league to places like Detroit, Tampa Bay, Philadelphia and Anaheim, California.

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

Ground zero for the shirtless outbreak was in St. Louis last Friday, when a club baseball team affiliated with Stephen F. Austin State University was in Alton, Illinois, for the National Club Baseball Division II World Series. The Cardinals offered tickets to the team, and 17 players attended.

That group started the fun, dozens of others joined and suddenly their were a couple hundred fans creating a ruckus in right field that helped propel the Cardinals to a 5-4 victory in 11 innings over the Kansas City Royals. Cardinals manager Oliver Marmol loved the energy so much that he bought tickets for the shirtless revelers for Saturday’s game and they returned.

Even the Cardinals’ mascot Fredbird joined in on the fun.

Now it might be the start of a tradition — more shirtless fans cheered for the Cardinals in Tuesday’s game against the Pirates. It certainly seems to be a boost for the club’s homefield advantage: 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. Another small group celebrated in Philadelphia as the Reds and Phillies played in the rain. Angels’ fans celebrated with a mix of joy and irritation, chanting for owner Arte Moreno to sell the team.

MLB certainly won’t complain about the recent attention. Attendance is up at big-league stadiums so far 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.

A wild feat in Washington

WASHINGTON — It was only a matter of time before Washington Nationals outfielder James Wood hit a grand slam.

But an inside-the-park shot, like the one Wood smashed in Tuesday’s 9-6 victory over the New York Mets?

“I didn’t think it would be like this,” Wood said. “That was a fun way to get it.”

Down 5-0, the Nationals loaded the bases with two outs in the second inning against Mets starter Nolan McLean. Wood hit a first-pitch sweeper to the opposite field, where it glanced off the leaping Nick Morabito’s arm and bounded into center.

“When I saw that, I kind of just knew it was a full-on sprint home,” the 23-year-old Wood said of his 53rd career home run. “That’s probably why my eyes got big.”