Chapman did a pair of forward rolls after striking out Martin Maldonado to complete a 4-3 win over the Milwaukee Brewers on Tuesday night. Chapman has been struggling lately, and celebrated his ninth save with somersaults toward home plate.
Baker has made sure that Chapman knows he was out of line.
"It's been addressed already and it's over," Baker said on Wednesday, before an afternoon game against the Brewers. "It won't happen again – ever. I know he's happy and things have been going poorly for him, but he's got to demonstrate in a different way."
Chapman, who speaks through a translator, declined to discuss it.
The Brewers were surprised to see Chapman's forward rolls, but Baker doesn't expect retaliation. He played three years with Brewers manager Ron Roenicke on the Los Angeles Dodgers.
Asked if he would tell Roenicke that he's handled the matter, Baker said, "I think that's between us and the Brewers, know what I mean? You know, Ron was my teammate. He knows me. He knows me very well. He knows how I am. He knows how I do things.
"Next subject."
Chapman's had an eventful first half of the season.
The hard-throwing Cuban was getting ready for the rotation during spring training when injuries wiped out the back end of the bullpen. With closer Ryan Madson and set-up men Bill Bray and Nick Masset hurt, Baker moved Chapman back into a set-up role.
Chapman pitched so well – no earned runs allowed in his first 24 appearances, a club record – that he moved into the closer's role. The left-hander has struggled in the last two weeks. He had given up game-losing homers against Cleveland then Minnesota in consecutive outings before his save on Tuesday night.
There have been several off-field problems as well.
Chapman was arrested for speeding – going 93 mph on an interstate – and driving with a suspended license in a suburb of Columbus, Ohio, in the early hours of May 21.
During a series in Pittsburgh a week later, an exotic dancer claimed she was tied up by an unknown assailant in Chapman's hotel room and robbed of $6,000 in jewelry while the pitcher was away. She has been charged with filing a false police report. Police said some of Chapman's items were stolen from the room.
Also, Chapman has been sued for $18 million by a Cuban-American who claims that before the pitcher defected from Cuba, he made false statements that resulted in the man being imprisoned.
Click here to see the video of Chapman somersaulting on the field >>