Castillo, an outfielder from Buffalo, New York, was a standout in Western New York at Lancaster High School in both baseball and football— even scoring a touchdown at Highmark Stadium, home of the Buffalo Bills. His rare combination of power and agility drew interest from MLB organizations. In the 2017 MLB Draft, the Milwaukee Brewers selected Castillo, who chose to sign rather than play college baseball at Oklahoma. 

The 26-year-old quickly became a leader in the clubhouse thanks to his fluency in both English and Spanish. In 2022, Castillo made his RailCats debut, playing in 47 games while posting a .318 batting average, seven home runs, and a .516 slugging percentage. The “Buffalo Basher” was named an All-Star in 2023 after fans voted him in as the final selection. Over 331 games with the RailCats, he has collected 336 hits, 162 RBI, and a .264 average. With this being his fifth season, Castillo will become the longest-tenured RailCats position player since Alex Crosby, who played five seasons from 2015 to 2019.