The incident at the Azadpur station happened at 8:20 pm after two men engaged in an argument at the ticket counter, CISF officials said.
The Central Industrial Security Force (CISF) personnel deployed at the station brought the two to the control room and asked them to pay the fine for creating trouble, they said.
But one of them, a 17-year-old resident of Wazirpur industrial area, called his associates to the station. Nearly 20 people reached the station soon and allegedly beat Delhi Police constable M L Meena, who was taking the two to the Kashmere Gate police station, the officials said.
The situation at the station was chaotic but metro rail services were not interrupted, they said.
The police said they have detained a few people and examining the next legal step. Senior officials of the CISF and the Delhi Police were examining the CCTV video of the incident, they added.
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