Defence attorney Jay Leiderman described the gesture as "very sweet", but prosecutor Jacqueline Bluth described the move as "absolutely inappropriate".
The Las Vegas trial has previously heard that War Machine told his porn star ex-girlfriend he would have to kill her as he stood over her helpless body and beat her for two hours.
In opening statements, the court heard how the fighter threatened to murder his former flame Christy Mack, as he mercilessly attacked the adult actress.
The brutal assault began when he burst into a bedroom and found Mack in bed with another man in August 2014.
After allegedly pummelling her new lover, the MMA fighter turned his anger on Mack, leaving her with a broken nose, missing teeth, fractured eye socket, leg injuries and a lacerated liver.
The 35-year-old is on trial for 34 felony charges against him, including kidnapping, attempted murder and multiple counts of sexual assault, all of which he pleaded not guilty.
Prosecutors began casting the former MMA fighter as violent in his relationship with the porn star and murderous when he found her asleep with another man in her bedroom.
In a rage, he had stood over Mack during the beating and told her "This is it. I've got to kill you now", reported the Las Vegas Review Journall.
Corey Thomas, the man who was in bed with Mack, told the court he thought he was going to die in the 12-minute battle with War Machine, where he was bitten and put in a choke hold by the expert fighter.
According to NEWS3LV, Thomas said: "He bit me there on the cheek and I could feel the bite.
"And once it registered I was getting bitten, then I put my hands back up to try to break him off my face and then he hit me on the arm.
"I'm looking up at the ceiling thinking to myself 'I'm going to die in Christy's bathroom. That's not how I'm going out.'"
Thomas said Mack's horrific injuries were ''the saddest [he] ever saw."
Thomas added: "When I was in hospital, Christy was in the room right next to me. Her eyes looked like they were peppered shut. Teeth gone."
War Machine, who said he would go by Koppenhaver in court, had a quiet defence attorney in Jay Leiderman.
Leiderman didn't deny during opening statements that a fight took place on that early August morning.
But he characterised Mack and Koppenhaver as "two damaged people" each with an adopted public name, deep image insecurities and a co-dependent relationship that revolved around sex, constant attention and internet personas that exploded into violence.
"It was a co-dependency that was bound to erupt at some time," Leiderman told the state court jury during opening statements in a trial expected to last two weeks.
If found guilty, Koppenhaver could get life in prison without parole.
"The two of them were swallowed up by the personas they had created for themselves," Leiderman said.
They met as performers on an adult film shoot. Koppenhaver legally changed his name to War Machine during his 19-fight MMA career, and he started a clothing line he called Alpha Male.
She had shortened her given name, Christine Mackinday, for her adult film career. She cheered ringside at his martial arts bouts. He became jealous of her professional sexual encounters.
The Associated Press usually doesn't identify alleged victims of sexual assault, but Mack gave the AP permission to use her name. She is expected to testify during the trial.
Prosecutor Jacqueline Bluth told jurors that Mack liked to be choked during sex, sometimes to unconsciousness. Leiderman said Mack had rape fantasies, and invited Koppenhaver to surprise her.
Thomas, a digital media company owner who is both taller and heavier than Koppenhaver, testified that he dated Mack for two months before Koppenhaver arrived unexpectedly, flipped on the bedroom lights and set upon him on the bed with rapid-fire punches and chokes that nearly left Thomas unconscious.
High school wrestling experience and a couple of years of unarmed defence training helped Thomas escape, he said, along with the presence of mind to ask Koppenhaver whether he was going to kill him or let him leave.
Thomas testified that he ended up with a broken nose, dislocated shoulder, scrapes and bruises, and bite marks on his face and arm. Koppenhaver let him go with a warning that if he went to the police, Koppenhaver would enlist friends who are Navy SEALs and Hells Angels bikers to hurt him, Thomas said.
Mack testified in 2014 that after Thomas left, Koppenhaver attacked her, leaving her with a broken nose, missing teeth, fractured eye socket, leg injuries and a lacerated liver.
She has said she drifted in and out of consciousness as she was beaten, kicked and groped sexually. She said she escaped when she thought Koppenhaver was in the kitchen fetching a knife to finish her off. She ran naked and bleeding to neighbours' homes.
Koppenhaver was arrested in the Los Angeles suburb of Simi Valley a week after the alleged attack.
He has been in Nevada state custody since that time, serving 1½ to four years in prison after his probation was revoked for a prior conviction in a 2009 attempted battery causing substantial bodily harm case involving a 21-year-old woman.
Koppenhaver made his Ultimate Fighting Championship debut in 2007, and he had a 14-5 record as a welterweight. His final fight was in 2013.
He was dropped by his fight promoter and his clothing line after Mack's accusations became public.
