Most fat people think weight is all that matters for force, but speed is critical too. I've seen big ass 350 pound samoans punch those force measuring things as hard as they can and barely do anything. Granted they have fists the size of hams and getting hit a couple times will send your brain bouncing around in your skull and knock you the fuck out, but its not as brutal as people think cause there's no speed there. I'd be much more worried about an average sized guy with big hands throwing really fast punches.
Look at mike tysons knockout highlights. Thats what speed is when combined with power. Deadly and terrifying