There's nothing that quite says summer like baseball.

A baseball field is a sanctuary for millions of boys and girls, moms and dads. From the working class to the white collar, from the Marine to the congressman, America's pastime has been a respite from the day-to-day grind for generations.

That's why Wednesday's shooting at a congressional baseball practice in a placid neighborhood in a Virginia suburb of Washington was so shocking.

"We were upbeat, getting ready for a game," Rep. Brad Wenstrup, R-Ohio, told NBC, "and then something like this happens, and you can't believe it."

Washington in recent years has been marred by acrimony and partisanship. And members of Congress have increasingly faced threats and hostility. There are few bipartisan traditions that have survived, but the Congressional Baseball Game is one of them.

Its peace and civility was shattered Wednesday morning when a gunman opened fire with what one witness described as a semiautomatic weapon in a local park on a warm sunny day, hitting Louisiana Rep. Steve Scalise and four others at the Republicans' practice the day before the big game.

The game is still on, scheduled to be played Thursday at Nationals Park. NPR's Susan Davis reports, per Rep. Martha McSally, R-Ariz., that when it was announced that the game would go on, it was met with cheers and applause.

Many outside Washington might be surprised that the game is even played, given the rancor and discontent that seems to define the political arena. But the game is more than a century old; the teams practice separately in the early mornings and come together to square off every year to raise money for charity.

Here's a little bit of the history:

-The game has been happening since 1909.

-Thursday's game will be a tiebreaker between the two teams. Each side has won 39, lost 39 and tied once. (It's the 57th annual game, but in some years multiple games were played.)

-The idea is "Senate and House members of each party team up to settle scores and solidify friendships off the floor and on the field," the Congressional Baseball Game's website notes.

-This year's charities are the Boys and Girls Clubs of Greater Washington, the Washington Literacy Center and the Nationals Dream Foundation, which supports academic, arts, nutrition and sports initiatives for Washington area youth. The game has raised as much as $500,000 in the past.

-The game hasn't happened every year. For a while, it was occurring biennially, and sometimes leaders complained it was getting in the way of legislative business.

-In 1958, House Speaker Sam Rayburn, for whom there's now a congressional building named, ended the game. He thought it had become "too physical."

-In 1962, the Capitol Hill newspaper Roll Call picked up sponsorship of the game and began awarding a trophy for a five-game series. That series was played 10 times; Republicans won eight of them.

-In recent years, Democrats have had more success, mostly because of one person — Louisiana Rep. Cedric Richmond. Richmond, who played college baseball at Morehouse, had been dominant until last year's game. Republicans broke a seven-year losing streak to Democrats in 2016. Richmond is now 43 and has had shoulder surgery. Before last year's game, where he gave up six runs in six innings, he was 5-0 with 45 strikeouts in just 27 innings work. Rep. Joe Barton of Texas, the coach of the GOP team, called Richmond " the best player, in my opinion, who's ever played in the game."

-Before Richmond, Steve Largent dominated the congressional baseball scene. The Republican was a former wide receiver for the Seattle Seahawks. He joined Congress in 1994, went 5-1 with a 2.44 earned-run average in his starts, leading Republicans to five wins in seven years. He left Congress to run for governor and was inducted into the Roll Call Congressional Baseball Hall of Fame in 2002.

-It won't be the first time the game was played after a tragedy, though nothing has touched the game this closely. Last year, Democrats wore rainbow wristbands for the victims of the Orlando nightclub shooting.

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