A driver who was asked by a paramedic in Worthing to move his car, attacked the NHS worker and then drove his vehicle at the ambulance.
Sussex Police said an ambulance on an emergency call was trying to get through Becket Road on Sunday, but the route was blocked by a Ford Fiesta.
The driver of the Fiesta was asked to move but instead he carried out the attack and drove off, officers added.
A 52-year-old man has been arrested and bailed until 20 December.
Police said the man was arrested on suspicion of common assault, dangerous driving and obstructing an emergency vehicle.
A spokesman for Sussex Police said the car was driven at the ambulance in a dangerous manner, but there was no collision between the vehicles.
Anyone who saw what happened has been asked to contact the force.
A spokesman for the ambulance service said: "South East Coast Ambulance Service NHS Trust takes any violence and abuse of its staff extremely seriously.
"Our staff deserve to be able to serve their local communities in safety and we always work with the police to seek the highest possible sanctions against those who are violent or abusive towards our staff.
"Ambulance clinicians have a vital role to perform and we seek motorists' patience and co-operation when we are responding to often life-threatening emergency calls."