Confirmed by an ESPN article released in 2007,
https://www.espn.com/mlb/story?id=2740570&src=desktop, Tatis was invited for spring training with the LA Dodgers in 2007 as a non-roster player. Because of this, he was probably given this green shirt with his in the Instagram post above for St Patrick's Day. This is a rare find because Tatis played for a few other teams throughout the years, including the Cardinals and the Padres, so it was a rare find to see not only a Dodgers Jersey with the last name 'Tatis' on it, but a green one.