Kneeing people in the groin may work well in comedy films but is actually very difficult to do and involves getting a bit too up close and personal in reality. Much easier and extremely effective, if all you want is enough time to get away from a situation, is a good, hard kick in the shin. Having played hours of football when l was a kid (jumpers for goalposts etc) I know how it feels to be kicked in the shin and it hurts, boy does it hurt, and certainly takes your mind off whatever you are doing at the time.