If i see a guy mobbed by a bunch of enemies, like 6 or 7, there's not much I can do to save them. The best thing I can hope for is to charge through them to stun them, knock them down and hopefully strike one with my axe.
When you're on foot though, and someone wonders out of your formation and gets surrounded, you can usually still get him saved if you're quick enough. Your guys tend to follow you, and if you manage to distract the enemies to focus on you instead, you can usually give the guy breathing space while your mates rush up to mob the enemies that venture too close.