The condition of Dheeraj Kumar is said to be serious, police said.
One of the four youths used to harass Dheeraj's sister every day when she was on her way to a a nearby institute where she is pursuing her BBA.
After the girl informed her family about this, Dheeraj opposed the harassment and got into a dispute with the youth, who later called his friends and thrashed him up, police said, adding that a case has been registered against the four youths and investigation is on.