At first, the Cards' star quarterback was jubilant -- he high-fived somebody -- but then his demeanor quickly changed after a man appeared to hit him in his face with an open hand.
Video shows Murray became upset -- and tried to identify the fan who appeared to tag him. Arizona players eventually raced in to intervene before things escalated.
A Las Vegas police spokesperson said on Monday cops are now investigating the matter -- saying a battery complaint was made at Allegiant Stadium at 6:26 PM.
"We do not provide victim names however the event you are requesting is a battery call alleging a spectator at the stadium struck a professional football player," the spokesperson told TMZ Sports. "A crime report was taken, and the suspect has not been identified. This is an ongoing investigation."