Other very insightful articles on this website outline how women can become abused by men. This is (by far) not the only time partners are abused! Men are also abused by women, and gay couples can abuse each other.
When the abuse is between a man and a woman it is more often true that the man is abused verbally and/or emotionally than physically due to the usual difference in physical size and strength. But because women are far more likely to report physical assault than are men, and police (sadly) often believe women more often than men when they have been called to a situation of assault, men are usually afraid to physically respond when they have been assaulted by a woman. She may “only” slap him across the face or kick him (or worse) but these actions are also considered to be assaults.
Consequently men can find themselves in a situation in which they are a) being physically assaulted and b) dare not respond even to protect themselves and c) may not be believed or taken seriously when they report the incident to the police. What is he to do?
Regardless of whether the man is being physically or emotionally abused he needs to first firmly inform his partner that this conduct is unacceptable, to not accept any responsibility for her abuse of power, and to act on his belief that he deserves to be treated better than that. This usually means leaving the situation and letting his partner know that the conversation will not continue until such time as she can be respectful toward him. If he has been physically injured, regardless of whether he is believed, he needs to report this to the police. This may be a key step to helping her to finally get help, even if she is never charged.
In order to be strong enough to act with self-respect he will need to believe that he does, indeed, deserve better. Anyone who is abused has usually endured a history of such, so often lacks this self-respect or self-esteem. Professional help is often needed if friends or family are unable to reach him.
The best way to address a man who is being abused in any form is to let him know of your concern, that you love him and that you believe he deserves better. If he responds well to this then you may be in a place to listen to him say what he is experiencing, being careful not to try to counter his sense of shame but to appreciate that he is willing to risk this with you. Then he may be open to doing something about his situation.
Regardless of the gender, abuse is degrading and undeserving. Anger is usually fear-based (e.g. a fear of the mate leaving the relationship).
Life can be much better.