Well, title explains it abit.
If player has 0 stars and does damage to a entity give him 1 star trough AddStars(1)
and if he already has 1 star, then return false.
So it will go like this:
player does damage to entity, give him 1 star if he does NOT have 1 already, elseif he has 1 star or more then dont do anything.
Should be simple, but I just cant find the function for entity taking damage.