>>17
That's a legitimate explanation, but there are a few problems with it based on their reaction.

If they had indeed seen it as an invasion of their territory, they would have behaved aggressively towards the usurper rather than the potential mate. Attacking the female would simply reduce their chances of mating at another time, while trying to eliminate competition would be more conducive to future reproduction.
Most herd(deer, gazelle, horses) and territorial mammals(wolves, lions) as well as the apes and chimpanzees from which humans are direct descendants have "mating rituals" where the males compete against each other for a chance to mate with the available females. In fact, males of species with "troop" organizations(lions, apes) will actually kill the offspring of the males that preceded them when they become the alpha male.
However, in the process of mating the females are in a position of power where they choose which males to mate with, and they are generally free from any physical danger themselves.

If the men in this situation were behaving according to the model followed by their close genetic relatives, it is odd that they would act out against the female. Thus, it can be concluded that although it is likely that they were angered by the intrusion, something other than territorial invasion incited them to act as they did - in fact, they were so affected that they behaved contrary to their instincts.
It seems that the males actually choose to eliminate themselves from the breeding pool because of the actions of the female, and they seem to have done so for emotional reasons.

I do not mean to insult the OP by referring to her as a "female" here - on the contrary, I am arguing against the idea that she and the men acted for purely animalistic reasons.