A good Samaritan was bitten and choked on the D train at Columbus Circle Saturday, in the latest off-the-rails subway attack.

The suspect was harassing a passenger on the uptown train around 5 p.m. when another straphanger intervened, police said.

The attacker turned his ire on the 20-year-old do-gooder, and attacked him with his mouth and hands, according to the NYPD.

Police arrested the alleged attacker, who was identified by sources as 44-year-old Billy Torres, while the victim went to the hospital for treatment of his injuries, police said. No charges have been announced as of late Saturday.

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The attack comes a day after four people were slashed and one was punched at three Manhattan stations in a 12-minute span, by a group of suspects on a subway crime spree.

The latest brazen attacks underground have MTA officials and many candidates for mayor calling on City Hall to beef up police presence in the subway.

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