u didn't specify if hes strong enuff to lift u and slam u on your head
if he isn't id suggest cornerning him in a corner and running at him full steam
u can easily flatten him with your huge belly and lay him lying on the floor.
Simple Answer:
Better technique, strategy, faster, outclass, etc, etc, etc.
In short. Be a better fighter.
Use technique and strategy
this ****** in my class how to beat him up fast? btw im 15 fatter and taller than him