The Sports Law Blog has two posts you should read about Tony Allen. One explains that this is serious (and remember, that's a lawyer talking):
Aggravated battery is an extremely serious charge. First consider the definition of criminal battery: the intentional and wrongful physical contact with a person without his consent, and that contact is injurious or offensive. Aggravated battery takes it a step further: it is a criminal battery accompanied by circumstances that make it especially eggregious, such as the use of a deadly weapon, or the fact that the victim suffered serious bodily harm, or the fact that the victim was in a vulnerable position. Under Illinois law, aggravated battery is a "Class 3 felony," meaning a conviction can carry a maximum punishment of not less than two years and not more than five years in prision.
The second post you should read is barely a half-hour old, and dips a little into Tony Allen's criminal history. If he's convicted, the riot and assault arrest when he was 19 could be a factor in sentencing. (Interestingly, Sports Law Blog can find no evidence Allen was seriously disciplined by Oklahoma State for that incident.)