Edward Bald heard the first rock shatter the window of a first-floor bedroom of his house on Quincy Street.
He reached for the shotgun he keeps on the top bunk of his bed.
"I sent a warning shot out the hole they already put in the window," said Bald, 61. "I hit one of them; I didn't know I actually hit him until I saw the blood in my backyard."
Bald's shot late Friday morning hit a 12-year-old boy who suffered non-life-threatening injuries, according to Buffalo Police.
"Detectives say the incident was not a random act," said Michael J. DeGeorge, a spokesman for the Buffalo Police Department.
Police and the Erie County District Attorney's Office continued to investigate the incident, DeGeorge said.
Buffalo Police had not charged anyone as of Friday, DeGeorge said.
The incident occurred a little before noon in the first block of Quincy Street, off Broadway, where many of the homes have boarded windows.
Bald said he called police to report the shooting and the attempted break-in. He said he doesn't think the person he shot with his .20-gauge shotgun was 12.
"If he is 12, he must have been born in a leap year or something," said Bald, adding that he didn't get a good look at the 12-year-old, who he said was wearing a dark hoodie. "I just got a glimpse of him."
The 12-year-old boy was taken to Erie County Medical Center by ambulance, Buffalo Police said.
Bald said he inherited the Quincy Street home from his grandparents, and has lived in the same house all his life.
During recent years, the street has declined, said Bald and three of his neighbors.
Bald talked about previous first-floor break-in attempts at his home that have resulted in a broken window and a slit screen.
"See what I mean about the bottom window frame?" Bald asked, walking into his backyard under the yellow crime tape put in place hours before by police.
"I put roses and poison oak over there along the backyard fence, so they can't get in my yard," Bald said.