The mainstream popularity increase in MMA has shed light on just how powerful and effective the art of Brazillian Jiu-Jitsu can be. Jiu-Jitsu teaches to bend like the willow instead of being stiff like the oak tree. Call it what you will BJJ/Submission Grappling/Judo etc in a nut shell its ground fighting and its incredibly effective.
Take a 220 pound muscular/athletic man with no training and put him in a combat situation with a 150 pound experienced ground fighter…. well lets just say id put my money on the little guy.