To those of you who think size is a huge advantage and you could maybe take a light weight professional boxer or some other trained fighter, I highly recommend a screening of
Fight Science. Take the guys who break bricks for a living. It goes into detail about how they generate more impact force than a sledge hammer, and how their bones remodel and thicken over time. Or the martial artists who can generate lethal force with a single blow because of how they coil and uncoil their body, and how quickly they can generate that force without ever loosing balance.
This is a common fallacy with professional athletes. We see guys on TV and think "Hey, I could do that!". No, you can't. These guys are elite athletes who've been perfecting their craft for thousands of years (martial artists).