A Pittsburg man who police say was punching a woman riding in his passenger seat Saturday is facing possible felony charges because a Good Samaritan took action.

Police arrested Stephen Evans, 35, on suspicion of felony domestic abuse after finding him in his black Mitsubishi convertible near the North Concord BART station on Port Chicago Highway, Concord police Sgt. Matt Morrissey said.

Evans appeared to be punching his female passenger while driving east on Highway 4 around 6:30 p.m. when another driver saw the commotion and followed the car, Morrissey said. When Evans exited at Port Chicago Highway, the eyewitness also followed him and continued to see punching, Morrissey said.

The car eventually stopped near the Oliveira Crossings shopping center off Oliveira road, and the female exited. The eyewitness stopped to help, and Evans drove off, Morrissey said. The woman's face was swollen and bruised, Morrissey said, but she refused medical treatment.

Police searching the area found Evans a short time later, Morrissey said.

Evans was taken to County Jail in Martinez, Morrissey said.

Rick Hurd covers crime. Contact him at 925-945-4780 and follow him on Twitter at Twitter.com/3rdERH.