My old roomate used to work as a bouncer, it's kind of the same way in that you need to be decisive with stopping girls from fighting. In his words:
Two guys will swing it out with their fists for maybe ten hits until someone intervenes and, unless a weapon is pulled, it's generally over, they'll go fume it off and won't cause more trouble.
Two girls? They go for crippling stuff, pulling hair, gouging eyes, biting, scratching, they usually have to be physically pulled apart by multiple people and even if they're separated from each other for 10+ minutes they'll still try to restart the fight the second they see each other again.
The cop was in the right stopping them as decisively as he could as quickly as he could.