Agree that it's terrible sportsmanship, since on this occasion it wasn't as if the batsman was blatantly stealing a yard (I know there have been other incidents when that's not been the case) and he wasn't warned. The law seems like an ass on this one, since I think they do say that the bowler mustn't be into his action before taking the bails off, so it acts like an incentive to do what the bowler's done here, namely to run in with the sole intention of mankading him. As a few have said, if he'd run in as if to bowl, the bat would probably have been behind the line.