A former Cincinnati Bengals defensive back visiting his grandmother in California was shot dead this week in her backyard, relatives said.

Terrell Roberts, who appeared in 23 games for the Bengals in 2003-04, was gunned down late Wednesday at a residence in Richmond, where an intruder entered the home, relatives told KPIX.

Roberts, 38, was “not mixed up in anything bad” and had no known enemies, relatives said.

No arrests have been made as of Thursday afternoon, but investigators were searching for a suspect described as a black male, about 20 to 35 years old, weighing roughly 250 pounds who was last seen wearing a black shirt, Richmond police Sgt. Enrik Melgoza told The Post.

Cops responded to a report of a shooting at about 4 p.m. Wednesday and found Roberts dead in the backyard with a gunshot wound to his chest. He was pronounced dead at the scene, Melgoza said.

The shooting stemmed from a dispute between the suspect and Roberts inside the home’s garage. The connection between the suspect and the former NFL player remained under investigation Thursday, according to Melgoza, who declined to discuss evidence recovered from the residence.

Roberts, a native of Berkeley, California, attended El Cerrito High School and Oregon State University before being signed by the Bengals in 2003. He was released by the team in the 2005 season.

News of Roberts’ death began spreading on social media early Thursday, prompting tributes from former teammates.

“Man am tired of waking up everyday to bad news,” retired defensive tackle Shaun Smith tweeted. “Another one of my former teammates [was] shot and killed rest easy Terrell Roberts one of the strongest DBs to play the game rest easy my boy.”

Current Oregon State coach Jonathan Smith was also a college teammate of Roberts.

“I’m crushed to hear the news of the passing of my teammate and friend Terrell Roberts,” Jonathan Smith tweeted. “Prayers to his family and friends during this difficult time.”