The 27-year-old corner outfielder is hitting a robust .290/.393/.432 in just over 300 plate appearances this season, good for a 138 wRC+ that ranks first on the team among players with at least 100 at-bats.
He's walking at an impressive 12.9% rate, is on pace to hit double-digit home runs and steals, and has supplied a healthy eight Outs Above Average (OAA) in left field this season. In other words, he's been doing everything well on the diamond.
Unfortunately, the Rookie of the Year race isn't just about what a player is or isn't doing. It's relative to how other rookies in the senior circuit are performing.