Billy Taub was an O.G. celebrity athlete star f***er of the first order. He put out a series of postcards in the early 1930s including this one with Ruth:
Rodine, early 1950s:

A premium but the same art:
Some signed:
Boxing does have some astounding PCs. Among my favorites:
As far as I can tell, this is the first boxing PC:
Jack Dempsey from Japan, promoting his serial "Daredevil Jack":
Interesting Cuban promotional PC signed from HOFer Kid Chocolate written to HOF broadcaster/promoter Cuco Conde
The Brown Bomber:
The Rock, pre-1951 PC
Float like a butterfly, sting like a bee:
No list would be complete for me w/o an Adam Hats. Billy Conn, PC and premium: