The clash started around 5.30 p.m. near Tilak Vihar colony in west Delhi after a motorcycle rider knocked down the boy who was flying a kite on the road, police said.
Police used tear gas and water cannons to disperse the two violent groups who also attacked policemen and torched their vehicles.
"During the clash, someone opened fire and the bullets hit three people. At least 15 others, including three policemen, also received injuries," said Additional Commissioner of Police V. Renganathan.
The official said just after the accident, the boy and the motorcycle rider were involved in a heated argument.
The boy's family members reached the spot and started manhandling with the motorcycle rider. Some sympathisers of the mobike rider came to his help and the two sides turned violent, police said.
A police team arrived at the spot but they were also attacked by mob, the official said.
"The protesters also burnt three police jeeps. We had to use tear gas and water cannons to disperse the mob. The situation is still tense," said the officer.