Or a man, for that matter.
Many men have been killed outright by a one punch blow to the head from another man. In fact, statistically afaik, the victims of one punch blows tend overwhelmingly to be other males, because the vast majority of men would never even dream of lifting a finger to a woman:
One-punch deaths: How lives are devastated by a single blow
While no official figures are available on one-punch deaths, the campaign group One Punch Can Kill has recorded more than 80 fatalities since 2007.
Many of the cases have attracted media attention - in large part because it seems extraordinary that one punch can kill.
Many one-punch killings involve young men, often in drink-fuelled, random acts of violence.
I recall one of my brother's friends had an altercation with a nightclub bouncer, who proceeded to give the guy a sudden left hook.
My brother's friend ended up in hospital with brain damage.
However, vis-a-vis a comment made by the OP, if my girlfriend assaulted me with a glass bottle or left actual bodily harm in the form of scars with an ashtray, I seriously doubt that I'd still remain in that relationship, personally speaking. It would be an immediate red-flag.
Physical abuse is physical abuse and in my book she would've had no right to do that, as it's a violation of my bodily integrity, no matter her gender.
Men are stronger and usually bigger with more muscle mass than women, so yes we have a far greater responsibility for gentleness and non-retaliation and any man that hits a woman (unless it's an accident and he's literally defending his life or at risk of being assaulted with a knife or something) is a beast as far as I'm concerned, but still it's never ever ok to assault anyone of any gender.