What is the congressional baseball game?

Gunfire erupted Wednesday morning at a Republican practice ahead of Thursday night's scheduled baseball game between GOP and Democratic lawmakers.

The game is an annual tradition that dates back to the early 20th century, with Thursday's game at Nationals Park slated to be the 80th meeting of the two teams. One of those shot, House Majority Whip Steve Scalise, R-La., has been an avid player in the game since getting elected to Congress in 2008.

The event raises money for local charities - more than $500,000 last year was split among the Boys and Girls Clubs of Greater Washington, Washington Literacy Center and the Washington Nationals Dream Foundation. The game allows lawmakers to engage their competitive athletic spirit while demonstrating their hometown pride, before a crowd that regularly hits about 10,000 fans.

There are no uniforms given out to either team. Instead, lawmakers wear the uniform of their local professional or collegiate team.

The Republicans have two coaches, longtime manager Rep. Joe Barton, R-Texas, and Rep. Roger Williams, R-Texas, a recent arrival to Congress with a deep history in baseball. One of those shot Wednesday was a staffer for Williams.

The Democratic manager is Rep. Mike Doyle, D-Pa., whose squad had won seven straight games until last year's narrow loss. The overall series is deadlocked at 39 wins each, with one tie.

The teams have a group of assistant coaches that include congressional aides, former aides and lobbyists who have expertise in the game. While the game itself is a highly secure environment - fans must pass through the magnometers to get into the stadium - the practices are not considered a secure event.

The only reason Capitol Police were on hand Wednesday to take down the shooter was because Scalise is the third-ranking member of House Republican leadership, a post that comes with a security detail that follows him most places.

Held every summer, practice for the game usually begins about two months or more ahead of the game, which can become a deeply competitive battle. Republicans, and their fans, sit on the first base side of Nationals Park, while Democrats take the third base side of the field and stands.

Two years ago, President Barack Obama attended a few innings of the game, staying in the dugouts with each team briefly.