Realmuto's hit struck the home-run sculpture in center field. Ozuna, who was on first base, misjudged the fly and retreated to first, and Realmuto trotted past him.
First-base umpire Mike DiMuro didn't see what happened, but the Brewers did. After Ozuna and Realmuto crossed the plate, Milwaukee manager Craig Counsell challenged the two-run homer, and the play was overturned.
Realmuto was credited with a single and an RBI and ruled out at second base. Ozuna was credited with a run, giving Miami a 1-0 lead.
The baserunning blunder ultimately did not affect the outcome of the game, which the Marlins won 4-1.
In the postgame clubhouse, Ozuna wore a T-shirt the Marlins hand out in such situations. It read, "I stink at baserunning."
"My mistake," Ozuna said. "I feel bad. I apologized."
"It's inconvenient it happened," Realmuto said. "But Marcell has apologized to me four or five times already. I love that guy. There are no hard feelings. We won. That's really all that matters."
The Brewers missed a similar blunder by an opponent earlier this season. The Cardinals' Randal Grichuk hit a two-run homer and passed teammate Brandon Moss rounding first base, but the Brewers didn't challenge, and the umpires also failed to see the mistake.
According to Retrosheet, the last major league player to lose a home run because of such a gaffe was Baltimore's Javy Lopez in 2006. It also happened to Lou Gehrig of the Yankees in 1931, when he finished the season tied with Babe Ruth for the major league home run title.
Said Realmuto, "I don't think it's going to cost me the home-run title."
Information from The Associated Press was used in this report.