According to KSAT.com,
He told officers he wasn't expecting anyone, so he didn't rush to answer it, but that's when he heard someone kick the door down.
Police said that's when he grabbed a gun.
"He was able to grab his handgun in the process of the three suspects breaking in the front door into his location," said officer Misty Floyd, San Antonio Police Department. "He was able to fire off several rounds. One of the rounds hit one of the suspects."
The wounded intruder, a 26-year-old man, was struck in the upper torso and was driven to the emergency room by his accomplices. He is expected to face charges if he survives.