Bill,
I get a lot of pics like that. After watching them over the years, I'm convinced that these are not really fights. It almost seems like the mature buck uses the young buck as a sparing partner preparing for more serious fights later in the season. I see these mismatches much more frequently early in the season. I sometimes see grooming activity both before and after the sparing. I think the younger bucks are more instinctively testing their strength rather than challenging the mature bucks. Most of the more serious fights I've seen are between much more evenly matched bucks and they typically occur a bit later in the year.
Thanks,
Jack