This isn’t a sleuthing post, because the caption information supplied by Getty Images gives it away:
New member of Chicago Cubs coaching staff, John (Buck) O’Neil, 51 (r), congratulates Cubs first baseman Ernie Banks after Banks slammed out 3 homers in the game with the Milwaukee Braves here 5/29. O’Neil was the first African American to coach in the Major Leagues.
This game happened Tuesday, May 29, 1962 at Wrigley Field. Buck O’Neil, one of the most famous of Negro League players, was indeed the first Black coach in Major League Baseball.