While on SCUBA in the Carib. damsels of all species will defend their territory almost to exhaustion/death. I believe this 'attitude' or behavior is a procreation instinct. When damsels spawn, the eggs number in the upper hundreds, maybe thousands. In nature, schools of fish will bombard the 'nest' and eat, eat, eat away. The damsels are programed to fight off the attackers, even though the attackers are always MUCH bigger that they.
I have been hovering 5 to 7 feet above a large coral head on SCUBA and have had Sargent Majors attack, and even bite at my hair and arms. It really is astonishing to witness.
So small, so tough.