The incident took place Wednesday night when the victim, Karan, was asleep in his house in Shahadra in east Delhi.
An orphan, he lived with his maternal grandmother Daya Sawant, 65, aunt and her two kids.
Karan tried to resist the eight robbers who struck at their house. The robbers first hit him with an iron pan and then threw him down from the second floor, police said.
Some neighbours rushed to help them and the robbers tried to flee, police said.
The neighbours managed to catch one of the robbers, identified as Kunal, 21, a resident of Shakarpur in east Delhi, police said.