In all reality...
Please, please, PLEASE do not make your hero try to kick a gun out of someone's hand. If a bad guy is standing close enough for the hero to kick the gun, he's close enough to see the hero's leg move before it's completely raised. And shoot the hero in the femoral artery.
Not a pleasant ending.
On groin strikes:
Evil guards will not immediately double over and fall, unless they're expecting it and trying to take some of the force out of the strike by bending before the strike makes full contact.
If they're not expecting it, the burst of anger and adrenaline they get ensures that they can do a lot of damage to the hero before they finally keel over.
I think this happens more because of a poor choice of words than someone trying to make a cool fight scene, but I'll address it anyways.
If a knife is pressed against the side of your hero's throat, do not make him "yank" back. Knives work using friction. So if the hero yanks back...when the knife is pressed firmly against him...
Well, bye-bye, hero.
Do not allow your heroes to be killed in such untimely fashion!
Prepare and have them take self-defense classes. :)