There was just an article on the news about a town that was horrified by the male mallards injuring and killing the female mallards to the point the town threw a party when spring was over (not even kidding).
Not at all uncommon when there are other competitive drakes in the area.
I repeat that in my experience mallard drakes form a strong pair bond and are not abusive to their mate unless their are other competitive drakes in the area. I would for sure closely monitor the pair and his actions.