We did an article on this! FightWrite: On Hair Pulling
You want a hairstyle that keeps the long hair tightly bound (skin tight) so that no opponent can get a good grip. A loose ponytail isn’t good enough. Modern “conventional” wisdom likes to assume that only girls are wussy enough to pull each others’ hair or that it’s “cheap”. It’s actually not true. Regardless of what is right or fair, both men and women will yank someone else around by their hair in a fight. The reason is that the hair is full of nerve endings, when yanked on their cause pain, and a good solid grip on someone’s head means that you can control where they go in a fight.
A character with long hair is going to need to keep their hair bound up and out of the way, or their opponent will snatch it and yank. The longer and looser the hair, the easier this is.
A ponytail, a loose braid, and even a loose bun will allow another character to simply walk up behind the character and take a hold of them, or grab it during a fight when they get in close enough. There’s no practical reason to ignore the hair, so most don’t.