All these years and I had no idea how packed with awesome Women's Flat Track Roller Derby is. I don't generally go for team sports (especially as a spectator), but the gals of Assassination City Roller Derby won me over. My mind is blown. Wikipedia will give you the basic overview: [link]

Assassination City: [link]
WFTDA leagues (so you can find one near you): [link]

During a demonstration at All-Con 2012, some of the players reviewed their list of injuries received... and one the list of injuries given. Still, despite how seriously they get into the competition, they seem to have a great deal of fun.