Do you girls find this behavior often? How does it make you feel? When do you feel safe and when not? Do you like being protected by men you don't know who insert themselves in that role, either by calming their own group or by physically protecting you and perhaps confronting another man?
If you're talking about situations where I actually feel threatened, then no, it doesn't happen often. For one thing, I'm not often in a situation like that alone, and besides, most men are perfectly fine. A bunch of rowdies at a football game may annoy the crap out of me, but I don't fear for my safety from them. The more isolated the scenario, the scarier.
Alcohol is a factor. Any group of men who have been drinking would make me nervous. I told a story on here some months ago about encountering a group of men on a dirt road out in the boonies. They'd been drinking and a few of them made crude remarks. That really scared me because one of them could have followed me and I had no place to escape to.
(ps--It's not just women who fear this type of situation. A drunken group of rednecks is threatening to anyone who isn't part of their group, whether it's a gay man or a hippie-type or someone from a different ethnic background.)
Gang-type attacks happen, but most assaults against women are carried out by lone men. I go on a little higher alert when I see a lone man who seems to be paying more attention to me than normal.
This is not to give the impression I walk around in constant fear. Only one man in a million is a psychopathic rapist. It's mostly a matter of being aware and avoiding certain types of situations. For that matter, if we want to talk about violence against women, husbands and boyfriends are statistically much more likely to commit these kinds of crimes. But that's another issue.
I've reached that point in life where I'm pretty much invisible to any man under 30.
I find I get more attention from young men now than ever before. I have no idea why. Maybe there's more attention being given to the "cougar" thing now, and they think they'll get some of it. It's possible too, that I'm totally misinterpreting their interest, but I don't think so. My daughters point it out to me. "Mom, that guy was so checking you out." It makes me chuckle.