As news of the shooting at a U.S. congressional baseball practice in Virginia rippled across the country, many observers may have wondered at the same question – why were Republicans playing baseball at 7 a.m. on a Wednesday morning?

The members of Congress were up bright and early swinging bats and running bases to prepare for the annual Congressional Baseball Game for Charity. The bipartisan ballgame between Senate and House members from both parties has taken place every year, with few breaks, since 1909.

According to the official website for the annual game, lawmakers don uniforms from their home states and districts as they compete against their party rivals.

“Senate and House members of each party team up to settle scores and solidify friendships off the floor and on the field,” the site states.

This year’s game is scheduled to take place on Thursday, at Nationals Park (the home of the Major League Baseball’s Washington Nationals) in Washington, D.C.

Proceeds from the event are donated to a number of charities including, The Washington Literacy Center, The Boys and Girls Club of Greater Washington and the Washington Nationals Dream Foundation.

Rep. Mo Brooks of Alabama, who witnessed the shooting that injured several people including House majority whip Steve Scalise of Louisiana, spoke with CNN about the annual charity event.

“It raises about US$600,000 for charity and we play it in the Washington Nationals’ baseball stadium. Frequently the President will come so it’s a pretty good time for all,” he said.

Sen. Rand Paul of Kentucky, who also witnessed the attack on Wednesday, also weighed in on the significance of the tradition.

“It’s really one of the best things we do. It’s a bipartisan thing. I’ve gotten to know many Democrats through this game. We joke around, it’s collegial, it’s for charity,” Paul told CNN.

“It’s a good thing. Who would want to kill people trying to do something good?”

The Republicans weren’t the only lawmakers playing ball on Wednesday morning. The Democrats were also meeting at another Washington-area neighbourhood ballpark when the shooting occurred.

Rep. Jared Polis of Colorado tweeted that their team practice had been cancelled after word of the attack spread.

“Thoughts and prayers w my Republican baseball friends this morning. Dem practice cancelled holding in dugout w security,” Polis wrote.

Rep. John Tener of Pennsylvania, a former professional baseball player, organized the inaugural game in 1909, according to game’s website.

Since that time, the congressional ballgame has been held almost every year with interruptions from the Great Depression, the Second World War and an intervention from House leadership.

In the past decade, the Democrats have dominated the annual competition thanks to the pitching talents of Louisiana Democrat Cedric L. Richmond, but the Republicans managed to break their seven-year losing streak in 2016.