sorry, can't go with you on this one. At no time should any professional athlete assault a fan in any sport. Fans are the reason those athletes have jobs, so if they want to voice their opinion about how they are playing, or even about their moms sexual exploits, thats what buying a ticket affords them. Any athlete who violates that should be dealt with harshly.
Now on the other hand, if the fan had assaulted the player first, either by touching him or dumping a beer on him or something, its game on. But a little verbal abuse is just part of being a pro and making the big bucks.
here is an example of the grey area of this topic: