San Francisco Giants starter Matt Cain left the game after three innings Wednesday night against the Colorado Rockies with a strained right hamstring.San Francisco Giants starting pitcher Matt Cain works against the Colorado Rockies in the first inning of a baseball game in Denver on Wednesday, May 21, 2014.San Francisco Giants starting pitcher Matt Cain, back, delivers a pitch while framed by Colorado Rockies batter Troy Tulowitzki, front left, and home plate umpire Adam Hamari in the first inning of a baseball game in Denver on Wednesday, May 21, 2014.