Still kinda new at this, but do young bucks rut before older bucks? I've seen several younger bucks chasing around but some of the older bucks I saw today were still grouped up.
The young bucks tend to get excited prematurely. The older bucks have played this game before. What you are seeing is the younger bucks chasing. The doe is typically not ready to breed, but the little buck doesn't realize it or just doesn't care. They will travel more, chase more, and harass the doe long before the big boys get interested.