Johnson High School in Huntsville, Alabama, Petty led his team to the state championship game and earned first-team Class 4A All-State honors.

[1] In his sophomore season, he won the Class 5A state title and was named tournament most valuable player (MVP).

He averaged 20.7 points, 7.7 rebounds and 5.6 assists per game, won his third consecutive Class 5A state title and became the third player to win Alabama Mr. Basketball twice.

[8] Sources: On November 17, 2017, in his third collegiate game, Petty scored a season-high 30 points and made a school-record 10 three-pointers in a 104–67 win over Alabama A&M.

[12] On January 19, 2019, in his sophomore season, Petty matched his career high of 30 points in a 71–68 loss to third-ranked Tennessee.

[12] On November 28, 2019, Petty recorded a then-career-high 34 points and 12 rebounds, his first career double-double, in a 104–89 loss to Iowa State at the Battle 4 Atlantis.

[16] Five days later, Petty shared SEC Player of the Week honors with Jair Bolden of South Carolina.

[27] Petty's father, John Sr., played basketball as a shooting guard for Buckhorn High School in New Market, Alabama.