A plain clothed police officer was injured when he tried to speak to a driver in a town centre car park in Horsham on Saturday (21 March).
The incident happened just after midday when the officer approached the car in the Swan Walk multi-storey car park. It drove away and he was knocked to the ground.
The injured officer was taken to East Surrey Hospital.
His injuries are not thought to be serious.
Anyone who saw what happened or who has any other information is asked to email 101@sussex.pnn.police.uk or phone 101, quoting Operation Bramshaw.
Alternatively they can contact the independent charity Crimestoppers without having to leave their name on 0800 555 111.