A police community support officer (PCSO) suffered a broken knee when he was struck by a quad bike which was then driven off.
The officer was knocked down on East Street in Loftus near Redcar at about 19:00 BST on Wednesday.
Cleveland Police said two bikes were seen driving dangerously, with the metal frame of one hitting the PCSO and knocking him to the ground.
Both riders then made off, the force said. Two men have been arrested.
The PCSO was taken to James Cook University Hospital where he received treatment.
The quad bikes are described as adult sized and dark in colour, with one rider on each bike, and police are appealing for witnesses or anyone who knows the whereabouts of the machines to get in touch.
A force spokeswoman said the two men, aged 20 and 28, that were "arrested in connection with the incident" have been released under investigation pending further inquiries.