The shooting occurred at about 4:15 p.m. near West 80th Street and South Damen Street on the city's South Side.
The boy was shot several times in the upper body, including in the head and back, in an alley, police said. He was pronounced dead at the scene.
Community activist Andrew Holmes was at the scene and said that he believes there were witnesses and is urging neighbors to come forward.
"This child should have been walking to school in the morning, not taking a ride to the medical examiner's office," Holmes said.
Police said an unknown number of people were gathered in the alley when an altercation started and resulted in gunfire, said Dean Andrews, Chicago police chief of detectives.
A neighbor told ABC7 that he was watching TV when he heard at least five shots. He ran out to find the boy laying on the ground with his basketball next to him.
Family members said the boy brought his basketball everywhere he went.
"I feel so bad, this baby could do no wrong," neighbor Raynetta Tyler said. "A 9-year old-kid. What could he have done wrong? There's nothing a 9 year old could do to deserve this."
Monday evening, police continue to canvas the neighborhood and search for surveillance video.
"That's not an accident," said Fr. Michael Pfleger, of St. Sabina Church on the South Side. "That's not a stray bullet. That's an execution."
Anyone with information is asked to call Chicago police at 312-747-8271.
A $6,000 reward is being offered for information about the shooting.