Zack was selected by the Oakland Athletics out of the University of Virginia in the second round of the 2021 draft. The All-American was named the first-team third baseman in the 2021 College World Series. After his first year in the minor league, he was ranked the second-best A’s prospect by Fangraphs.

Despite being sidelined seven weeks with a torn labrum, the Delaware native played at both the Double-A and Triple-A levels in 2022. Zack made his major league debut with Oakland on July 14, 2023 and hit an RBI double in his second at bat.

Zack set an Athletics franchise record in 2023 by hitting his 10th home run in his 35th major-league game.

Gelof played second base for Team Israel in the 2023 World Baseball Classic.