Mechanics question: Beating an NPC to death with another NPC Ran in to a situation during a session today where my Wookie decided to grab a storm trooper, and throw him in to another storm trooper. 

My DM told me he couldn't find a mechanic for that, so while i could grab one trooper, he couldn't think of a way to dish out damage to both. 

I didn't want to provoke a debate in a game, and left it for researching later. So, is there a "throw dude in to another dude" mechanic we don't know about? 