Switch to Single- point AF!
Subjects wearing a peaked cap or hat are often photographed out of focus as the multi- point AF locks onto the headwear protruding in front of the face. The easiest solution is to switch to single- point AF and focus on one of the subject's eyes. It's worth using a reflector in these situations too, to remove shade caused by the peak.
Inset above: Multi- point AF focuses on the hat's peak. Main: Single- point AF ensures perfect focus on the face, while a white reflector gives much needed light.