In most cases, this is true, but there are a few ballplayers who FIRST played in MLB and then later joined a Negro Leagues team. How was this possible?
It involved either a Native American or light-skinned Cuban ballplayer who, because of the pigment of their skin, could navigate between the segregated worlds of white and black baseball. The list includes:
Confirmed Players
Reported But Not Confirmed
*Negro League team reported in "Playing America's Game"
**Negro League team reported in "Only the Ball was White"
**
NOTE ON EUSEBIO "PAPA" GONZALES
As mentioned above, neither Seamheads.com nor the SABR Bio includes a reference to Gonzales with the 1931 Royal Giants, but you can see below that he (with his signature ears) is standing next to Hall of Fame pitcher Andy Cooper in the team photo taken upon their arrival in Honolulu, Hawaii.
And on May 30, 1931, Gonzalez is in the Giants' lineup playing second base and batting second.
Source: Negro Giants Troupe Ekes Out Close 5 to 4 Verdict from Braves in Keen Fray, Nippu Jiji / 日布時事, (Honolulu, HI), May 31, 1931, 12. https://hojishinbun.hoover.org/en/newspapers/tnj19310531-01.1.12
**
There might be others who played in MLB first before competing with a Negro Leagues team. If and when they are identified, this page will be updated accordingly.
##