The key thing is - are the ewes standing for him, even encouraging him, or is he just attempting to mount and they are moving away?
If the latter, then it's probably as SteveHants says, just overenthusiasm. (I have one tup gives me concern every year as he marks every bottom within 30 hours - but he's just a tryer, thinks a ewe who says No means Maybe!

)
However, if the ewes are seeking his attention and/or standing for him, then it sounds as thiugh they are not in lamb. It could be the tup is firing blanks, or that something has caused the ewes to not implant / abort.