Ill. R. Evid. 405
Comment
Specific instances of a person's conduct as proof of a person's character or trait of character are not generally admissible as proof that the person acted in conformity therewith. Specific instances of a person's conduct are admissible, however, under Rule 405(b)(1), as proof of a person's character or a trait of character only in those limited cases (such as negligent entrustment, negligent hiring, and certain defamation actions), when a person's character or a trait of character is an essential element of a charge, claim, or defense. Specific instances of conduct are also admissible under Rule 405(b)(2) in criminal homicide or battery cases when the accused raises the theory of self-defense and there is conflicting evidence as to whether the alleged victim was the aggressor.