'Jersey Shore' Star Ronnie Ortiz-Magro's Baby Mama Claims He Hit Her

'Jersey Shore' star Ronnie Ortiz-Magro's baby mama told cops the reality star struck her multiple times during their domestic dispute ... but cops concluded she was the one in the wrong.

Jen Harley was arrested Sunday in Vegas for domestic battery after she allegedly attacked Ronnie while the two were driving home and then dragged him with her car.

According to the police report -- obtained by TMZ -- cops say they found Harley on the side of the road after a passerby called in to report a fight between the two.

Harley told cops she was driving and Ronnie was in the passenger's seat. She says Ronnie became aggressive, reaching for the steering wheel and hitting her multiple times. Harley claims she pulled over, took their 3-month-old daughter out of the car and tried waving down other drivers for help.

The police report states officers observed minor cuts, scratches and dried blood on Jen. The report also details Ronnie's injuries ... saying he sustained cuts to his mouth, arms and road-rash. Ronnie told officers Jen struck him 2 to 5 times with her fist, he got in the driver's seat once she got out and took off.