PHILADELPHIA -- There is a select group with the Nationals into which, if you meet the criteria, you are welcomed.

The requirements are specific, and admission isn’t easy to attain. Once you’re in, though, there is a ceremony and a shirt to commemorate the honor. It’s only for those who stay ready and deliver at a moment’s notice -- off the bench.

“We were like, let’s just make ‘Studs off the Bench,’” infielder Jordy Mercer explained. “Because that’s what we are.”

This season, backup players have been sporting red T-shirts with the acronym “S.O.B.” spelled out across the chest. The founding members are Mercer, first baseman Ryan Zimmerman, catcher Alex Avila and outfielders Yadiel Hernandez and Andrew Stevenson. They don’t play every day, but when they do, they make an impact.

“It’s hard to come off the bench in the big leagues,” Zimmerman said. “It’s hard to pinch-hit. It’s hard to be productive. We’ve kind of taken it as a challenge, and we’re going to go at it together as a group.”

The Nats’ pinch-hitters entered Friday with a National League-best .818 OPS and .284 batting average -- 42 points higher than the second-ranked Mets. They also held the second-best on-base percentage (.348) and slugging percentage (.469).

Stevenson is tied for second among all pinch-hitters in batting average (.429), and he is tied for fourth in OBP and slugging. Additionally, Hernandez, Stevenson and Zimmerman rank in the top 10 in the league in pinch-hits.

“They’ve been unbelievable -- coming off the bench and putting balls in play and hitting balls hard,” manager Dave Martinez said. “They take pride in it. … Zim, Jordy Mercer, those guys have been awesome at getting some of those young guys prepared to hit, to get that one at-bat which typically comes in a big moment.”

The group of bench players spends an abundance of time together during games in the batting cages, staying loose in case they get called upon. They play games to keep the environment fun, and they’ve come up with their own inside references that are displayed on the shirts.

Mercer credits assistant hitting coach Pat Roessler for inspiring the concept. Symbolizing a sense of pride, the players have been seen donning their shirts during batting practice and in Zoom press conferences.

“I wear mine every day,” Mercer said. “The first thing I put on when I get to the field is my ‘S.O.B.’ shirt. I want to be recognized. I want to be, ‘Hey, this is an S.O.B.’”

The group motivates each other, too. Take Avila’s 2-for-3 afternoon against the Orioles on May 23 as an example. He had gone hitless in his previous two starts, and all of the other members had recorded at least one hit in the Nationals’ previous game.

“I was kind of feeling left out,” Avila said at the time. “All the other S.O.B.’s were getting hits, and I figured I got to join in.”

The original group has been expanding the S.O.B. membership in recent weeks. Those who contribute in a pinch-hit situation -- whether they are usually a starter or an everyday bench player -- can earn a spot in the club. Josh Harrison, Starlin Castro and Luis García are among the honorees who have been presented with a shirt in a ceremony held in front of the other members. There also is a box full of T-shirts ready for the next players who qualify.

“You’ve got to earn it,” Zimmerman said. “We don’t just give these shirts away.”

The players have been surprised by the popularity of the apparel, and there is a chance there could be more to come this season. For now, though, the S.O.B.s are keeping their plans to themselves and their circle exclusive.

“It’s a very sacred club,” Mercer said.