As the "bigger guy" I can tell you the smaller guys who give me the most trouble are mobile, agile and have better cardio conditioning. I've been in many matches where I've had the weight and reach advantage neutralized by some little 'skeeter who would stay just out of reach and run me ragged until he could sense fatigue weakening me. Then he'd move it and take control, slipping, parrying and
countering. Really sad to watch...