I have only seen an all out fight once. I have seen several sparring matches and quick bumps of the antlers but only one real fight. I was on a ridge overlooking a small bottom (select cut pine). The understory was starting to come back so it was somewhat thick in the bottom. I heard what sounded like leaves being pushed and then it sounded like a bull dozer was coming through the woods. Trees/limbs were breaking and it was an all out brawl. I could see the deer pushing back and forth but never had a shot on either of them. They were probably 150 yard through the understory. This lasted for a good 10 minutes. About the time I decided to get down to get a clear shot they stopped fighting. I killed the 11 point that was fighting that day on the next weekend using a tending grunt. I hit it twice and he ran straight up the hill like a freight train on a mission.
Last year I was sitting in another select cut pine stand and just over the hill from me (no more than 60 yards) I had a fight break out. I immediately started climbing down once I realized what was going on. I got on the ground and worked my way to that area. About half way there they stopped fighting. Never saw the deer but it sounded just like the fight referenced above. .
