Tulsa police are investigating after an off-duty officer heckled NASCAR star Tony Stewart and was confronted by the driver.

The confrontation happened Friday night at the weeklong Chili Bowl dirt-track racing event at the Tulsa Expo Center. Cellphone videos from fans posted online shortly afterward show Stewart and the fan locking hands and engaging in heated conversation.

The Tulsa County Sheriff's Office says the heckler was Cpl. Kyle Hess with the sheriff's office, and an investigation has begun.

The videos show Stewart going into the stands. Hess fell backward after a security guard stepped between the two, though Stewart continued to talk to a seated Hess.