What was wrong with Fick hitting the ball out of Karros hand at 1st?

[BigGamesOnly]

I hear the commentators for the Cubs/Braves game saying that when a runner slides into 2nd base it's ok to knock him down and when a runner goes into home it's ok to hit the ball out of the catcher's glove. Why then is it not alright to hit the ball out of a 1st baseman's glove???

 

[bosox1086]

I don't know. Maybe because it's illegal.