I'll add that when I think about women being hit, I think of domestic violence, where women are vastly more likely than men to be victims. I don't think it particularly sexist to point that out.
Brodski basically made my point for me.
Just because it's not popularly thought that men are domestic abuse victims does not mean that women are more likely to suffer. In Oscar's case, he didn't wind up and wail on the woman in question, he responded to her attack with a slap of his own. Hardly an overwhelming response.
Regardless, my point is that our society views women as being so frail that even though they serve on the front lines of many armed forces (and have for decades), they are still not viewed in the same manner as men. If Oscar had hit/slapped a man in the same situation, would you all have responded that he's a "man beater"? Likely not.
This is what makes it sexist. Women are just as able to injure a man as a man is able to injure a woman (not all men are big, strapping Jersey-shore type douches

).
Here's the first link Google found for "Domestic Violence Ratio Male to Female":
http://www.csulb.edu/~mfiebert/assault.htm
The Summary of the article:
This bibliography examines 271 scholarly investigations: 211 empirical studies and 60 reviews and/or analyses, which demonstrate that women are as physically aggressive, or more aggressive, than men in their relationships with their spouses or male partners. The aggregate sample size in the reviewed studies exceeds 365,000.
So there are studies that show women are at least as likely to abuse their spouse as men. Given this statistic, one would think it sexist to label a man a "wife beater" when defending himself/returning in kind.
It brings to mind the joke: "Sleep with 100 girls, no one cares. Sleep with one goat, and all the rest of your life you're a goat-f'r." Show's a bias, no?
Check the "Tiger crashed his car" thread in this forum for a story involving the possibility of female on male domestic abuse.