A 15-year-old boy was stabbed during an after-school robbery at a suburban high school and died at a hospital early Saturday, authorities said.

Michael Alguera was playing handball with two friends on a court at Hempstead High School on Friday afternoon when they were confronted by as many as nine people, some of them masked, said police in Long Island's Nassau County.

The attackers, possibly gang members, robbed the boys of a cell phone and an MP3 player, then stabbed Alguera in the torso, police said. He died at Mercy Medical Center in Rockville Centre, officers said.

The boy's companions, ages 15 and 16, were not hurt.

No one had been arrested, police said.

A man who identified himself as Alguera's cousin, Alexander Flor, said he was a "good kid."

"He was just playing handball," he said.