Eyewitnesses said members of the Shiv Sena beat up unmarried couples on the city's promenade as police watched.
The incident has caused outrage, prompting politicians to protest  in the state assembly on Thursday.
A police inspector has been suspended and six other officers have been transferred out of Kerala state.
Chief Minister Pinarayi Vijayan said the officers had been punished for dereliction of duty.
The Shiv Sena has previously attacked Valentine's Day celebrations in India and says that young couples "flaunting" their relationships is "totally contrary to Indian culture".
"The police did not act when it happened. That's a grave mistake. This group has no significant presence in the state," Mr Vijayan said.
He added that the culprits had been identified and would be punished.
The cane-wielding Shiv Sena members had arrived on Marine Drive promenade with a banner warning against "love under the umbrella" after informing the media of their intentions.
Seven Indian policemen have been punished for allowing far-right Hindu nationalists to attack young couples in the southern city of Cochin.