It has been reported that Boston Bruin forward Nathan Horton will not be suspended after he sprayed a Tampa Bay Lightining fan with a water bottle then threw the bottle at him.
After the Lightning disposed of the Bruins 5-4 in Game 6, fans littered the ice with noisemakers, which were given away for free by the team. As Horton left the ice, he leaned down behind the boards and grabbed a water bottle. He then sprayed a fan (who appeared to be heckling another player) then threw the watter bottle at him.
From a legal standpoint, spraying a fan with water then throwing the bottle at him could constitute criminal assault, as well as the tort (suing for money) of assault (reasonable apprehension of harm) and battery (where contact is actually made).
As far as a defence goes, Horton could argue provocation. The noisemakers were thrown on to the ice, and in some cases hit or came close to hitting players. However, if players could use provocation in these circumstances as a defence, we might routinely see players climb into the stands and go after fans (perhaps hit them with their own shoe, a la Mike Milbury).
Self-defence would also be another defence to battery. That would be tough here since you need to show that there was a real fear of physical injury. That doesn't seem to be the case here.
It's important for players to stay out of the stands.