Recognized as a top collegiate prospect entering high school, Hassell committed to play college baseball at the University of Tennessee in October of his freshman year.

[1] Hassell was named the Williamson County baseball player of the year again, as well as first team all-State by USA Today and an Underclass All-American by MaxPreps as a sophomore after batting .416 with nine doubles, six home runs and 52 RBIs.

[2][3][4] As a junior, Hassell was named the Tennessee Gatorade Player of the Year after batting .423 with 14 home runs, eight doubles, 36 RBIs and 22 stolen bases while also posting a 5-2 record with a 1.07 ERA and 113 strikeouts to 21 walks in 59 innings pitched.

[10] Hassell entered his senior season as one of the top high school prospects for the upcoming MLB draft and was named a preseason All-American by Baseball America.

[22] On August 2, 2022, Hassell, along with CJ Abrams, Luke Voit, MacKenzie Gore, James Wood, and Jarlín Susana were traded to the Washington Nationals in exchange for Juan Soto and Josh Bell.