A teenager's arm was severed after police say he tried to steal a pair of sneakers from a man in Brooklyn.

It happened yesterday afternoon on East 86th Street near Avenue M in Canarsie. Investigators say 17-year-old Zachary Sam arranged to meet 39-year-old Philipp Pierre to buy a pair of Air Jordan sneakers.

They say once Sam got inside the car, he allegedly pulled out a gun, demanded the shoes and then ran off.

Pierre then drove his car towards Sam and hit him, severing Sam's arm.

The 17-year-old then got on a MTA bus, but was pulled off the bus by Pierre.

Sam then tried to run away but collapsed from such a serious injury.

He was taken to Brookdale University Hospital, but it's unknown if doctors were able to re-attach his arm.

Sam is facing charges of robbery and criminal possession of a weapon, and Pierre was charged with attempted murder.