Attacks from the rear can come in many forms. Here we have a hair pull but it could easily be a lapel grab. The concept here is that regardless of attack, control his hands and immediately turn to face the attacker. The most common mistake in these attacks is to try and break free by going forward. This, unfortunately, gives the attacker more room and opportunity to pull you to the floor.
Once you have turned to face the attacker, we have demonstrated here an elbow strike. You could easily utilize any form of attack that came naturally to you, be it a thumb attack or a knee strike to the groin.