I watched a couple of braggin' bucks fighting one time. With horns engaged, they charged back and forth, maybe 50 to 75 yards with each engagement.
Fast? Folks, I had a serious case of the jaw-drops! If he has to, a buck can run backwards as fast as most dogs can run forward.
Realize, though, that unless there's some reason like the fight, a buck's gonna spin and run forward. I wouldn't call running backwards a preferred method of travel...
, Art