This is common with an Action Girl, Amazonian Beauty, Cute Bruiser, or Lady of War.
A violently protective girlfriend essentially acts like a much younger Mama Bear, except her Berserk Button is harm to her mate rather than to the kids; note that this inverts the expectation that the boyfriend is violently protective of the girlfriend (which may still be the case).
Girls are everywhere and many of them are open to fuck buddy relationships, short-term flings, and one-night stands if you catch them at the right time in their lives.
Bars and parties are notorious hunting grounds, but you can be bold anywhere.
A Non-Action Guy or dudes otherwise incompetent in combat seem to attract these women.
Most types of The Woobie (except a Jerkass Woobie who hasn't revealed his woobie side and Woobie, Destroyer of Worlds) also draw the attention of these types of women out of an instinct to ease their suffering.
Girls and guys are looking for roughly the same thing, and many have happily found satisfaction together in a casual fuck buddy relationship.
If you are married and looking and want to have an out of town affair or a quick fling you can easily find local NSA fuck buddies for sex as often as you want.
If you are looking for sexy local men, you will not be surprised to know there is a wide range of local hot men for you to choose from.
Sometimes a Butch Lesbian will act this way about her girlfriend due to the stereotype of being stronger and more "dominant", though a Lipstick Lesbian shouldn't be underestimated either.
Personalities associated with it include Plucky Girl (who may or may not fight but is likely to be protective anyway), Tsundere (who is apt to go into rage mode when said lover is threatened despite not being able to stand them half the time) and Yandere (who is likely to bring out the Ax-Crazy in response to anyone threatening what she feels is hers).