well dunt fight unless you have to. And you should know these people better then us. Anylze them, if you hit the leader will they

1. be shocked and back off
2. gang up on you

Depending on their reaction you gotta know how to deal with them.
If 1, i say punch down their leader, pick up the trash bag and throw him into the gang, they'll tuck intheir tail and run off.

if 2, take my advice and smash down the leader, pick up a chair and aim for the head of the biggest guys. The small sissies wont do much once they see their *back-up* is gone.

and one last word, if your doing this to protect your friend then I think its cool as long as no serious injuries are done.

but if you and your friend are planning this as a way to advertise yourself as the big boys in school, dunt do it. Personally Im a firm believer or energy, and I believe that doing anything for selfish reasons will backfire on you.