Police responded to Donovan Catholic High School in Toms River late Tuesday afternoon where officers found the teen on a field outside the school with the javelin impaled in the teen's right thigh.
There was no sign of bleeding and the Pine Beach resident was able to talk with medical responders, police said.
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"The javelin was cut by Toms River Fire Department members to allow for the safe transport to the hospital, said town spokeswoman Jillian Messina. "He was transported to Jersey Shore University Medical Center in Neptune."
It was not clear if the boy is a student at the school or if he was participating in the event.
No other information was available.