Getty Images says:
Second baseman Robby Thompson of the San Francisco Giants throws the ball as a player for the Chicago Cubs sits on the ground near the base bag.
Well, yes. The “player for the Chicago Cubs” does appear to be sitting on the ground, but obviously that’s not his intention, the runner is sliding in what is a clear attempt to break up a double play. It’s further obvious that’s a pitcher, because back in the day, pitchers wore jackets on the basepaths. Ostensibly this was to keep their arms warm.
Getty also helpfully said this photo was taken in 1991.