Street vendors thrashed a police officer and a constable in Loni town here, authorities said.
The local police station received information about a fight between two groups of street vendors late on Thursday night.
When Sub Inspector Sukh Pal Singh and Constable Sanjiv Kumar reached the spot and tried to calm the rival groups, members of one group attacked them.
Singh sustained injuries from sharp instruments. Locals carried the profusely bleeding officer and admitted him to a hospital where he was discharged after receiving first aid.
Constable Kumar sustained minor injuries and did not need to be hospitalised.
After returning from the hospital, Singh lodged a complaint against the assailants numbering around 20.
Police picked up most of the accused from their residences late on Thursday night.
"They have been detained for questioning," said Superintendent of Police (Rural) R.P. Pandey.