Police said Malaichamy (35),who is the local secretary of the party tried to enter the polling booth with the "DMDK flag colour shawl" but a police official at the spot asked him to remove it,leading to an altercation.
Police sources said the DMDK activist pushed a police man following which constable Solairaj hit and pushed him down.
He suffered injuries in the head and had been hospitalised, sources said.
They dispersed after police officials assured them that action would be taken against the constable.
A case has been registered against the constable and the functionary, police added.