Exactly, Bill. That's essentially why you don't see the big boys play spare much with each other. It's typically 2 youngsters or a youngster and a mature buck. Mature bucks seem to be fine play sparing with the youngsters, as they control that situation and don't seem concerned with it getting out of hand...and if it does, they'll be the one drawing blood. 2 mature bucks is a recipe for things getting out of control and resulting in a good blood letting on both sides.
I've said it before, but I don't think most truly grasp how nasty and life threatening true fights are between 2 mature bucks. As I type, there are 4, 4.5+ yr old bucks that I know of, just on the properties I'm managing that were either killed fighting (1) or at very high risk of death this winter because of injuries I'm at least 90% sure they received while fighting (3). I'm hoping 2 of them are able to limp through and make it, but 1 of them is so gimped up and lost so much weight from it already that there's no realistic hope of his survival, meaning the best case is that only 2 mature bucks on the grounds I manage will have died from fighting last season, which would be a great year for me. Combine the grounds I manage and one is looking at a yearly average of between 2500-4500 acres. I'd say 3-7 die from fighting each year.
Mature buck fights are nasty and I've come to strongly believe that they are no where near as frequent and are far more life threatening than most believe. In fact, I'm convinced that more mature bucks than not try to avoid them, if they can...When it most often gets nasty is when another mature buck tries to claim a section of a reigning King's ground. So long as they all have their own corner of the world to dominate, I've come to believe that pitifully few have the desire to get in real fights, as they are big enough to draw blood and it isn't a game anymore to them.