Hodgkins v. Peterson, 355 F.3d 1048, 1061 (7th Cir. 2004);
BeVier v. Hucal, 806 F.2d 123, 127-28 (7th Cir. 1986); Ramirez
v. City of Buena Park, 560 F.3d 1012, 1023-24 (9th Cir. 2009);
Logsdon v. Hains, 492 F.3d 334, 341 (6th Cir. 2007), cert.
denied, 129 S. Ct. 35 (2008). In Illinois, a person commits
a battery if he intentionally or knowingly without legal
justification (1) causes bodily harm to another or (2) makes
physical contact of an insulting or provoking nature.
. 5/12-3. The existence of a legal justifi-
cation for a battery is not an element of the offense, but
rather is an affirmative defense. People v. Meor, No. 106122,
2009 WL 1578527, at *3 (Ill. June 4, 2009); Simmons, 26
F.3d at 654 (citing Illinois law). Although Officer Grice
“may not ignore conclusively established evidence of the
existence of an affirmative defense,” the Fourth Amend-
ment imposes no duty to investigate whether a defense
is valid. Hodgkins, 355 F.3d at 1061; Humphrey v. Staszak,
148 F.3d 719, 724 (7th Cir. 1998); Fridley v. Horrighs,
291 F.3d 867, 874 (6th Cir. 2002).
Here, Guyton told Officer Grice that McBride had hit her
in the head, and Grice saw that her eye was slightly
swollen and that she had a small scratch on her forehead.
These facts certainly establish reason to believe that
McBride had intentionally made physical contact with
Guyton and caused her bodily harm or made provoking
contact. See Simmons, 26 F.3d at 654 (noting that victim’s
testimony may establish probable cause). At summary
judgment McBride submitted no evidence suggesting
that Grice had reason to doubt Guyton’s statements,
and Grice had more than Guyton’s statements to go on: he
saw Guyton’s injuries and watched the two of them