Bob Horner said he was looking away when his client, who is on trial for murder, grabbed a heavy metal chair and flung it across the courtroom.
He said the crash of the chair's landing was so loud that he initially thought someone in the audience might have shot at his client.
"I heard this enormous bang," said Horner, who is a partner in a Beverly Hills-based law firm. "I tell you, the bang wasn’t even done and I had dropped to the floor and rolled up under the table."
Authorities said the chair struck the detective and grazed Deputy Dist. Atty. Hilary Williams, who was prosecuting the case.
The blow knocked down the detective, who was treated for a bruise to the head at Los Angeles County-USC Medical Center, according to Los Angeles Police Cmdr. Andrew Smith.
Smith said the detective is assigned to the department's Force Investigation Division, but the murder case stemmed from her time as a detective in South Los Angeles' 77th Street police station.
Horner identified the detective as Myra Kellum. He said a gurney was brought to the courtroom to take her to the hospital.
Horner's client, Jesus Mendez, is charged with murder during the commission of a robbery in the April 19, 2012, slaying of Jamie Sharif Mohammad Abuawad.
The murder trial began last week in Department 134 of the downtown criminal courts building on Temple Street and was expected to wrap up in the next few days, Horner said.
Wednesday's attack took place about 10:30 a.m. as the judge and attorneys were preparing for a new day in the trial. The jury, Horner said, was in another room when Mendez threw the chair.
After hearing the loud crash, Horner said he looked around and saw the courtroom's bailiff on top of his client.
"I thought he was shielding him, not restraining him," Horner said. "In a blink of an eye, there were 20 sheriff's [deputies] in that room. They were four-feet deep on top of my client, stacked on him one on top of the other. It looked like they were playing dog-pile, like when you were kid."
Horner said he plans to ask Superior Court Judge Ronald H. Rose, who was present when the attack occurred, to declare a mistrial in the case. He said the request is likely to be denied.
But the attorney said he also will declare that he believes his client is incompetent to stand trial.
"This behavior is completely irrational and unprovoked," Horner said. "I think he needs to be sent off for a psychiatric evaluation."
Times staff writers Joseph Serna and Paresh Dave contributed to this report.