The fans are at fault for this - period.
Regardless of what happens on the field/court in any sport, fans should not be throwing things.
Throwing an object at an athlete that has adrenaline pumping through him is like poking a raging bull with a cattle prod.
Players scuffle and fight all the time - that does not entitle any fan to throw objects at the players.
A perfect example is baseball where many players have been hit by
batteries being thrown by fans. That's assault and IMHO the player has a right to defend himself.
How about I come watch you work and start throwing stuff at you?
Was Aretst right in doing so? Maybe, maybe not - that's going to vary from person to person.
The whole situation is a shame.