They evade, talk about staying out of reach, getting backup, or managing calls so that fighting isn't necessary. Fact is, if a young male weighing 180 jumps her, a female cop doesn't have a chance. Usually, not at all. Cops seldom do anything requiring physical strength. The authority of the badge usually produces compliance.
Bad guys know that if they resist one cop, thirty more show up, and some carry shotguns.
I've gone on many calls with tiny little women, and they've had no trouble. The rub is that occasionally things do get physical. Usually it's not a big deal. For example, the drunk gets obstreperous. It takes a couple of minutes for a small woman to get backup, and she does.