The man wore an authentic Kansas City Monarch jersey, and the sight of it drew a smile and a light laugh from the 94-year-old O'Neil, one of the most famous players to ever wear the Negro League franchise's colors.
"You're my hero," the man tells O'Neil.
The flattery didn't go to waste on O'Neil, whose smile broadened as he told the stranger, "That's all right. We're going to have a good time here."
But everywhere O'Neil goes, people have a good time. In his role as the unofficial ambassador of "black baseball," he stands as the last recognizable standard-bearer for a league that surely was its own.
He will represent that league and the 17 personalities from it who will be inducted this weekend into the National Baseball Hall of Fame. The regret, in some people's mind, is that the affable O'Neil won't be among them.
"Obviously, everybody loves Buck O'Neil," said Dale Petroskey, president of the Hall of Fame. "I love Buck O'Neil. How can you not love Buck O'Neil? So were we surprised he wasn't elected?
"Yeah, I think a lot of people were surprised."
Yet O'Neil seemed unwilling to dwell on the oversight. He shrugged it off as he does any negative that people might attach to anything. Call him an optimist, because that's about as good a description of O'Neil as anybody can come up with.
He's also a proud man, and his pride showed as he talked about his contemporaries from the Negro Leagues and his predecessors from the pre-Negro League era. Even now, he still basks in the glow of their success.
No success might be bigger than a spot in Cooperstown.
"This is actually outstanding," he said. "The fact that they're going to put 17 Negro League ballplayers in the Hall of Fame, at once -- oh, man, this is just actually the top of the ladder for me. Yeah, top of the ladder."
O'Neil said he'd been lucky enough to play against everybody on the list of inductees, and those he didn't play with, he knew of their reputation. He and his Negro League brethren talked about them. They spread stories about these men -- and one woman -- and their deeds, and those stories are what have built the legends of men like Sol White, Frank Grant, Ben Taylor or Pete Hill, at least for people who have an interest in "black baseball."
It's those legends, which a $250,000 research study that Major League Baseball funded help authenticate, that are being honored this weekend in Cooperstown.
"Man, this is gonna be something," O'Neil said before the official kick of induction weekend.
As he spoke, he displayed not an ounce of bitterness over his not being among the 17.
"Everybody was surprised, because they thought I was a shoo-in," he said. "But having been on the Hall of Fame Veterans Committee for 20 years, I knew what could happen."
Slight or not, he will stand up Sunday at the induction ceremony and speak on behalf of the entire group of Negro Leaguers, none of whom are alive today.
"All the guys who were supposed to be in Cooperstown, they're putting in at one time," he said. "That's what they were doing with this committee."
Justice B. Hill is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.