You probably saw the end of that fight (assuming you mean the one where he gets kicked in the face, his eyes roll back, and he kind of falls blankly to the canvas) which was like half an hour or more into it, and both guys were completely gassed after going all out. It just boiled down to the other guy having better cardio, and being able to bring the big kicks against him without even having to worry. Coleman was against the fence because he was getting too tired to stand.
That would have been Coleman's fight with Pete Williams. Pete was not a boxer per se, he was one of Ken Shamrock's Lions Den guys. Just a good all around fighter with good cardio.