After an overthrown pass from Colin Kaepernick, Michael Crabtree did what in any pickup football game would be considered good manners: he hurled the ball back. He was whistled for unsportsmanlike conduct. Maybe he forgot to yell, "heads!"
The flag had to be thrown—the ball plunked Tampa's Lavonte David back at the line of scrimmage. (It happens at 0:18 of the video.) But can't they cut Crabtree some slack for flinging a football from the Bucs' 10 all the way back to his own 30 or so? That's really freaking impressive.