It depends upon the individuals involved. I only weighed 175 lbs. once upon a time, and I fought and beat men bigger than 250 lbs. of all races. I recall one bout when I was just learning boxing and had no karate lessons yet. It was with a 260 lbs. man who was 7" taller. I was so quick and skillful that he could not even touch me with his "haymakers". He put all of his strength and weight into every punch. I evaded one and struck back knocking him down. Then, I just slugged it out with neither of us blocking. He could not hurt me at all, and I knocked him out early in the first round. After seeing that, my next opponents were scared of me. One man said he had just as well punch the wall as to punch me, because he could not hurt either of us but just hurt his hands. As you see, if it is me as a 175 lbs. teenager versus a 250 lbs. black man, I could demolish him quickly, but he could not hurt me at all. With other individuals, the outcome will be different, of course. In general, the well-trained man has an advantage over an untrained man. Many martial arts are about beating bigger and stronger opponents.