Honestly, this one’s non-gendered. Remembering that Michi and I have vastly different histories with hand to hand training, we both got almost identical instruction on how to deal with someone grabbing you from behind.
If the attacker grabs someone under the arms, then the victim should hunch forward, and pull their feet up. This forces the attacker to actually take the victim’s weight. When this happens, and they start to roll forward, the victim puts their feet back on the ground and propels themselves back up, into their attacker.
If the attacker grabs over the arms, like a bear hug. The victim makes a fist with one hand, and wraps the other hand over it. (I’ve also been told to interlace the fingers, instead of making a fist, with this technique.)
They straighten their arms so they’re forming a wedge shape. Now, the victim drives their fist up and away from their body (without bending their elbows). When this disrupts the attacker’s grip, the victim shifts their hips out of the way, and they drive their elbow back down into the attacker’s stomach.
If the attacker only grabs the victim’s arms or wrists, then they’re either an idiot or untrained. Quickly twisting the arm or wrist while pulling away from the attacker’s palm will break most grabs. This is one of the first things that will get covered in most self defense classes.
One last outstanding possibility, if the victim is being held as a human shield, the best option is (usually) to go completely limp. This forces their attacker to decide between abandoning them or trying to drag 150-200lbs of dead weight around.
No, even 50 extra pounds of dead weight are a pain for someone in decent physical condition. I was being a little flippant when I said 150-200lbs, but the fact is, an 85lb teenage girl who goes limp is still going to be a real pain in the ass for someone trying to use her as a human shield.
There are ways to pick someone up and carry them off, but the usual human shield setup doesn’t work for any of those.