You're walking around with your bata, they get attacked and are about to die, you're doing just fine not having taken any damage, so you rescue them from danger and the attackers start hitting you instead. It is essentially you grabbing your buddy and throwing them behind you so that you can act as the new tank.
In that game, it was a specific skill, but perhaps for SD it could be a roll based on your unarmed combat and str/agil/perc? Not sure about the details there. I'm sure staff could come up with a reasonable roll calculation.
If successful, you absorb the attacks from whoever was attacking your target. If more than one attacker is present, you basically roll for each attacker, so there's a chance you don't take all the heat off of your ally. If you completely fail, your buddy is still getting pwnt and you've wasted valuable fighting time!
It adds a layer of complexity to combat that currently doesn't exist and could mix things up in a fun way.
Some details to hash out would be:
1) If rescued, does the rescue-ee maintain their target? Do they stop attacking all together? (I'd say no, they fight on)
2) When attempting a rescue, is it automatic like disarm or does it happen more like posture changing and take a round or so to accomplish?(my suggestion would be it takes a round)
3) When rescuing, should you lose a round of combat all together whether you fail or succeed? (probably)