He did so because the boy was wearing a Big Baller Brand shirt.
The Greek Freak met up with the fans Sunday night, after the Bucks beat the Nets 109-94 at the Barclays Center in Brooklyn. He walked out to the meet-and-greet, welcomed by a raucous applause from a crowd of Greek fans.
After talking to the group, he signed a ton of autographs. At one point, he turned back and said: "Get this guy a shirt, man," referencing the boy wearing a white Big Baller Brand sweatshirt.
"We've gotta switch this," Antetokounmpo said.
He pulled off his two sweatshirts and separated them, giving the boy his shirt, which read: "Greek Freak."
"Make sure you wear that shirt, man," Antetokounmpo said.
"I'll wear it every day," the boy said.
Another boy in the audience said he should have worn his Big Baller Brand shirt. Sweathshirts on the Big Baller Brand website are mostly sold for $100. Los Angles Lakers rookie Lonzo Ball's signature shoes can be had for about $500.
Antetokounmpo had 16 points, eight rebounds and four assists in the Bucks' victory.