The incident occurred in when Karstens, with three innings of scoreless relief under his belt, came to the plate to lead off the inning. A high-and-inside, first-pitch fastball from Smith nailed Karstens near the left elbow.
The incident might have gone without consequence if not for what had happened in a game between these two teams back on April 27. It was after that game that the Brewers claimed Karstens purposefully hit Ryan Braun in the outfielder's first at-bat after homering off the right-hander.
Afterward, Braun made it quite clear in speaking about the incident that he saw definite intent behind Karstens' pitch that hit him.
"It's rare for Major League pitchers to miss that much with a fastball," Braun said after that game.
Karstens was fined an undisclosed amount, though not suspended, shortly after, and Milwaukee pitchers proceeded to hit three Pirates hitters in the following day's game. And though Karstens had come up to bat in the inning immediately after hitting Braun, he was not hit then.
That helps to explain why Karstens immediately took exception to Smith's pitch on Monday and shared a few choice words with the reliever as he slowly headed toward first. He obviously felt that he had been hit in retaliation for what had transpired three months earlier.
"I was kind of expecting it," Karstens said. "They felt like they had to do what they had to do, I guess. They had a chance to hit me in Milwaukee and didn't take it. They hit a few of our guys in the time and got [Ryan Doumit] in the first inning."
While Karstens stared at Smith, Brewers catcher Jason Kendall immediately followed him up the line and put his arms around him as if to restrain him. That prompted home-plate umpire Wally Bell to attempt to separate the two and both dugouts and bullpens immediately dumped onto the field.
"From what a lot of guys have said and I've seen on TV, you either go or you don't go, I guess," Smith said. "It just makes a big mess if you stand and yell. You either go or you don't go, is what they say."
"[I] just told him to go to first base or go to the pitcher," Kendall later said. "That's baseball."
Brewers first baseman Prince Fielder had to pick up Kendall to pull him away from the melee, while pitching coach Joe Kerrigan restrained Karstens. According to Kendall, Kerrigan further infuriated the former Pirates catcher by exchanging words with him during the tussle.
"It was fine until Dave Kerwin," Kendall said, referring to Kerrigan. Kendall continued to call Kerrigan by that incorrect name -- seemingly on purpose -- even after being promptly corrected.
"I can take a lot, but I'm not going to get yelled at," he continued. "Dave Kerwin started yelling at me...."
When asked what he thought made Kerrigan so mad, Kendall responded: "I don't know. Dave Kerwin? I have no idea."
No one ended up being ejected from the game after the brief dust-up was broken up, though it was quite clear afterward the Pirates manager John Russell was still livid over what he saw as intentional payback so far after the initial incident.
"They had a chance to get [Karstens] in a game he pitched," said Russell, whose team snapped a 17-game losing streak against the Brewers with Monday's win. "For them to wait two months.... The biggest thing was that Jeff went out and hit the next inning and they're going to wait and do it now? I don't understand that. They made such a big deal about it, but they had their opportunity and they're going to wait until they're getting beat and do it tonight? I really didn't understand what the reasoning is behind that."
Russell had planned to have Karstens return to pitch in the ninth, but when Karstens began stiffening up a bit in the area where he was hit, the decision was made not to send him out for a fourth inning of work.
"We just didn't feel like it was time for him to go back out there," Russell said.
Before he began the final inning, Pirates reliever Jesse Chavez was warned by Bell that he would be tossed if he were to retaliate. The clubs have two more games remaining in this series and will face each other another six times later in the season.
In the six games played so far, a total of nine hitters have been hit by pitches.
"I'm sure there's going to be warnings before the game tomorrow," Brewers manager Ken Macha said. "They're going to look back at everything that has happened so far this season. I'm sure there will be warnings before the game."
Jenifer Langosch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.