Absolutely not -- not if your son is a very young minor and it has nothing to do with coaching.  Was your son injured? Did he have physical bruises? If not, it may be harder to prove criminal assault/battery but there is also the process through civil court to determine (burden of proof is lower) if the coach is liable for any physical damage/injury to your son and also mental suffering. Keep in mind, oftentimes coaches do have more reason to have physical contact with their students but it doesn't mean that very aggressive pushing that is beyond simple coaching should be tolerated.

Try www.attorneypages.com to look for a lawyer and you can probably check his or her record at the Illinois State Bar.