With Reds catcher Tucker Barnhart batting, the count was 2-0 when Welke signaled to Mattingly to quit arguing from the dugout. The incident was initiated by a previous pitch, when an appeal to third-base umpire Pat Hoberg didn't go Miami's way.
Welke appealed to Hoberg on Barnhart's check swing. When the at-bat resumed, and Miami right-hander David Phelps was prepared to throw his third pitch, Mattingly was tossed.
Before heading to the clubhouse, Mattingly exchanged a few more words near home plate with Welke.
"He's got our backs," Phelps said. "From Day 1 of Spring Training, we've known that. He's gone out of his way to prove that to us, and show us that. When we're up or we're down, he's going to be fighting for us."
The ejection was Mattingly's third of the season, and it came with the Marlins and Reds tied at 1.
"He talked to us the first day of Spring Training, all he asked is effort," Phelps said. "If we give him effort, he can battle to the end of the world for us. He's also giving us that effort back. Even when we've been in some of our worst stretches, he's still been a guy that has been a constant presence for us. That's what we need in this clubhouse."
Bench coach Tim Wallach assumed Miami's managing duties.