The hamstring (also known as the biceps femoris, semitendinosus, and semimembranosus muscles if you want to sound fancy) is notorious for its variability in how injuries affect players. Some are out for the season, others might grab it slightly while walking off the pitch to justify a leisurely, clock-burning pace for an 80th minute substitution (as has been demonstrated beautifully by the consummate professional, Clint Dempsey, independent of his March 2015 injury). Considering it’s the most common injury in soccer players, there are a lot of questions about it. Like, what’s the hamstring do anyway? Why do soccer players seem so prone to injuring it in the first place?