If I didn't know better, I would guess that this is
@dirtynine's project:
The colors have a twofold meaning: One, they are the colors of the team (duh). Two, they are the color of the US flag, Boston having been one of the most important locations in the American Revolutionary War. The eight stars represent the Sox eight World Series wins. The circle containing the logo represents a baseball, and the sport in general, and the cross on the background represents the Catholic roots of the city.
My other favorite:
MIAMI MARLINS The arrangement of the flag is inspired by the official flag of Miami, with the Marlins' logo replacing the seal of the city in the middle of the tricolor. The colors are the team logo colors with an attempt to put them in a similar arrangement to the logo. They also represent a blue ocean with the sun rising (yellow sun, orange sky). The two stars represent the Marlins' victories in the World Series!
Anyone who can make the Marlins branding concepts attractive deserves a medal.
Edit: If someone wants to x-post this into the Main Board, please do so. I didn't know where it belonged (General MLB Discussion?).