(CNN) -- As the world knows, peace can sometimes be fleeting.
One-time basketball bad boy Ron Artest, who changed his name to Metta World Peace and said it was meaningful and inspirational, was ejected Sunday from the Los Angeles Lakers-Oklahoma City Thunder game for hitting James Harden in the head with his elbow.
After scoring against the Thunder in the second quarter, World Peace was cheering his own shot when he hit the Oklahoma City guard in the back of the head, knocking him down.
Harden was on the floor for several minutes, and did not return to the game after being diagnosed with a concussion, according to the Thunder.
World Peace was ejected from the game and faces possible suspension. The Lakers won 114-106 over the Thunder in double overtime.
"During that play I just dunked on (Kevin Durant) and (Serge) Ibaka, and I got really emotional and excited. It was unfortunate that James had to get hit with an unintentional elbow," World Peace told reporters after the game.
"I hope he's OK. The Thunder, they're playing for a championship this year, so I hope that he's OK and I apologize to the Thunder and to James Harden," he said.
Hours later, World Peace tweeted that he watched the replay again: "Oooo .. My celebration of the dunk really was too much ... Didn't even see James ... Omg... Looks bad."
Harden told ABC's Lisa Salters he had "a little bit of a headache."
On Monday, the Thunder said Harden was undergoing testing.
"Harden participated in a series of limited activities per NBA guidelines, but has additional steps that must be taken under the league-mandated concussion policy before he can make his return to the court," the team statement said. "He will be re-evaluated tomorrow and is currently listed as day-to-day."
World Peace's act was called "disgraceful" by game commentators, and sports analysts said the behavior was reminiscent of the ball player they once knew as Ron Artest.
"He has gone to such lengths to rehabilitate his image, and to revert back to this? He lost control," said Michael Wilbon, an ESPN analyst.
Sports fans were baffled, some even amused, when World Peace announced last year that he planned to legally change his name from Ron Artest.
"Ron Artest has contemplated the name change for years and always knew that he wanted his last name to be World Peace. But it took many years of research and soul searching to find a first name that was both personally meaningful and inspirational," his publicist said at the time.
Back when World Peace was still Artest and playing for the Indiana Pacers, he made headlines in 2004 for his role in a brawl between players and fans at a Pacers-Pistons game after somebody threw a drink on him.
The NBA suspended Artest for 86 games.
Fast forward to September 2011, when Artest announced the name change.
Even before it was finalized by the court, World Peace was working on making the world a more peaceful place.
In 2011, he raffled off his 2010 NBA Championship ring to help mentally ill youths. For his work with the youth, he was given the NBA's citizenship award for philanthropic work.
A star turn on "Dancing With the Stars" garnered the basketball player a new legion of fans.
But in the world, peace sometimes comes with a price: The NBA is now reviewing World Peace's less than peaceable actions.