It's easy to get hit from behind when fighting more than one opponent. One way to prevent this is by pushing over as many enemies as you can until there's only one left standing. Attack the standing opponent for a while and then push him over when another one gets back up. Now attack the person who got up and also push him down when another gets up. Keep doing this so you keep as many on the ground as possible and only have to worry about one or two enemies at a time.
Another trick for fighting multiple opponents is to use itching powder. Throw the itching powder at one of the people you are fighting and beat them up while they're scratching themselves. You should be able to get their health down to very low before they stop itching.