Piniella told the outfielder to take off his uniform and sent him home during the Cubs' 5-4 Interleague win over the White Sox after Bradley threw his helmet and tossed a Gatorade cooler in the dugout following a bad at-bat.
Bradley had struck out in the first and the fourth innings, then flew out to left for the second out in the sixth. He threw a fit in the dugout, and Piniella decided to discipline the outfielder.
"I told him to take his uniform off," Piniella said. "He threw his helmet and smashed the water cooler and there was water flying all over. I told him to take his uniform off and go home.
"I followed him up to the clubhouse and we exchanged some words. I don't like when those things happen, but I was tired of watching it."
Piniella said Bradley's actions have been a "common occurrence."
"I've looked the other way a lot," Piniella said, "and I'm done with it."
This season, Bradley's first in Chicago, has not gone well. He was batting .237 overall, and had an embarrassing incident June 12 against Minnesota at Wrigley Field. In that game, he hit a two-run double in the sixth, but also made a baserunning gaffe that inning, lost a ball in the sun in the seventh, and was charged with an error in the eighth when he caught a ball for the second out and threw it to a fan in the bleachers. Someone got a souvenir, and the Twins handed the Cubs a 7-4 Interleague loss.
Cubs general manager Jim Hendry said he would talk to the outfielder, who signed a three-year, $30 million contract with the team this offseason.
"It's something I promise won't be happening again," Hendry said of Bradley's tantrum.
Piniella originally had planned to give Bradley Friday off because of the switch-hitter's struggles against right-handed pitchers. After the game, Piniella said he would put Bradley's name in the lineup Saturday. They'll talk first.
Did Bradley say anything to Piniella?
"He didn't have anything to say," Piniella said. "We exchanged some words. I'm not happy this happened, but at the same time, it's time."
Cubs outfielder Alfonso Soriano said he'd never seen anything like what was apparently an ugly exchange between the two.
"It's the first time I've seen a manager fight with a player, get mad with the player," Soriano said. "Sometimes you can get mad, but not like that.
"I hope [Bradley] comes back and he can help the team to win. If he's not that way, we don't need him. We have 25 players, we have to be on the same page. If he's not 100 percent to help the team to win, we don't need him. If he's 100 percent and he comes and wants to play, he's more than welcome."
Cubs catcher Geovany Soto has had his first-half struggles, and recognized the signs of frustration.
"[Bradley] looks like he's a little frustrated with his at-bats," Soto said. "God knows, he wants to come in here and tear it up and help us win. The first two months, it is a grind and everybody knows he's trying 110 percent to get out of it. I have faith he'll come around."
Hendry expects the Cubs to put the incident behind them and move forward. He said other players on the team have had frustrating seasons -- Derrek Lee struggled in the first month, Mike Fontenot was batting .219 -- but they've always put the team first.
"All you want is for people to fight through their problems and stay with team goals," Hendry said. "That's not only what we expect, but that's what we demand."
Said Soriano: "Everybody gets frustrated here because we're not playing the way we're supposed to play."
But this isn't Bradley's first incident involving his temper. In his first at-bat at Wrigley Field on April 16, he was called out on strikes, argued the call, and was ejected.
"I think he's a great guy," Soriano said. "The only problem is his attitude sometimes in the game, I think a lot of people don't like that, but that's him."
"He's frustrated," Lee said of Bradley. "He's a guy who's had success and it's not working out and he's working his butt off. He's just waiting for it to click for him, and it isn't clicking. I'm sure it's frustrating.
"I'm sure Milton will be here tomorrow, he'll be playing, and he'll be fine. We'll move on."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.