How realistic do the sound effects for movie fights sound?

Think back to the last time you saw a street fight or an imbroglio in the school yard. If you’ve managed to miss that delight, think of a Mixed Martial Arts, Ultimate Fighter or a Professional Boxing match. Did you hear sounds like Oughahh!, Eughaaaaggg!!! Owrkerrough!!! and so on? Actually, fist fights are pretty silent events for the most part, aren’t they? So why does it seem right that movie fights are always accompanied by a sound track so far over the top it should leave the entire audience in hysterics?