Some fans are make personally attacking the player. I think commenting on a player's poor performance is quite different between publicly wishing the player would get hurt i.e. The team would be better off if Beck got hurt. I wish someone would knock Jamaal out of the game. I also think that some of these could be direct messages to the player with comments wishing that they would quit the team or something similar.

I think saying that "Beck can't hit a WR in stride this game" is completely ok for a fan to say.