That was the weakest headbutt I ever saw,and it was telegraphed big time,but that big dude could scrap.
Hard to hurt a guy that size unless you out crazy him and poke his eyes out or rip off his balls. 
if you can get him down on all fours stamp on his hands and break them.
I once saw a doorman do this to a huge guy outside a club, big guy kicked off , doorman wrestled him down and broke both his hands stamping on them, fights pretty much over then