I use to collect stamps. Babe Didrikson Zaharias in 1981 was the first US sports figure to be honored on a stamp. Babe Ruth had to wait until 1983 to get his stamp. Jim Thorpe, 1984. Bobby Jones, 1981 and 1998. Red Grange, 2003. US stamps were pretty dull until about 1970 -- ancient presidents, great causes, statehood anniversaries, flags, and Christmas.
One problem was the rule that you had to be dead for five or ten years to get on a US stamp. That's gone now, but I don't think any living person has been on a stamp yet. Living people tend to be too controversial.
Belgium issued this whole sheet of Belgian billiard stars. That's Raymond Ceulemans in the middle.