As an example. . . I may rob someone (snatch purse and run). Can the victim and by standers attack me without penalty? I was leaving!

Generally speaking, there is such a thing as use of force in defense of property. The applicable statute is as follows:   (720 ILCS 5/7-3) (from Ch. 38, par. 7-3)    Sec. 7-3. Use of force in defense of other property.     (a) A person is justified in the use of force against another when and to the extent that he reasonably believes that such conduct is necessary to prevent or terminate such other's trespass on or other tortious or criminal interference with either real property (other than a dwelling) or personal property, lawfully in his possession or in the possession of another who is a member of his immediate family or household or of a person whose property he has a legal duty to protect. However, he is justified in the use of force which is intended or likely to cause death or great bodily harm only if he reasonably believes that such force is necessary to prevent the commission of a forcible felony.    (b) In no case shall any act involving the use of force justified under this Section give rise to any claim or liability brought by or on behalf of any person acting within the definition of "aggressor" set forth in Section 7-4 of this Article, or the estate, spouse, or other family member of such a person, against the person or estate of the person using such justified force, unless the use of force involves willful or wanton misconduct.