The American Enterprise Institute (AEI) is a heavyweight in the think tank world, but it also a powerhouse in a lesser-known area: softball.
AEI's "Right Swing Conspiracy" just won the Think Tank Softball League (TTSL) championship, defeating the Roosevelt Institute's "Roosevelt Rough Riders" 17-15 in an extra-inning game. It was AEI's first-ever TTSL title. Here is a picture of the champs.
The TTSL is a summer-time, co-ed think tank league in the Washington, DC area. The teams are mostly from area think tanks, but also include representation from a number of government agencies and private firms. There are around 40 teams in the league.
Here is a 2010 list of the different think tanks involved, along with their team names. Here is an NPR piece from 2008 on the TTSL.
The softball league is so popular that some think tanks, such as AEI and the venerable Brookings Institution, tout it as a job benefit.
A few newspapers occasionally mention TTSL happenings (although your humble Think Tank Watch may have wider coverage). [Fun fact: The Washington Post noted in 2011 that Michelle Flournoy, Co-founder and CEO of Center for a New American Security (CNAS), "wasn't the best" softball player in the TTSL.]