Mobley is the son of Ronald and Pamela Mobley and grew up in the Washington Heights neighborhood of Worcester, Massachusetts. As a child he always begged his mother to go to the playground where he would play basketball against teenagers. Mobley developed into a star at St. Peter-Marian High School and averaged 28.2 points, 10.1 rebounds, and 7.3 assists per game as a senior. He led the team to the Central Massachusetts Division 1 title game and earned 2012 Hometeam Player of the Year honors and was a finalist for Massachusetts Gatorade Player of the Year award. He opted to spend a postgraduate year at Worcester Academy and developed into a good scorer after Rene Castro was injured. Besides Castro, who later played against Mobley at Duquesne, Mobley played alongside several future Division 1 players at Worcester Academy: Darryl Reynolds, Matt Cimino and Matt Panaggio.
College career
Mobley began his college career at Central Connecticut State and averaged 6.8 points per game in his freshman season. He increased his scoring to 17.2 points per game as a sophomore and earned Second-team All-Northeast Conference honors. After the season he decided to transfer to St. Bonaventure after developing a relationship with coach Mark Schmidt, sitting out a season per NCAA regulations. Mobley had a season-high 34 points and set a St. Bonaventure record with nine 3-pointers in a loss to VCU on February 4, 2017. On February 22, Mobley finished with 31 points and 10 rebounds to lead the Bonnies past St. Joseph’s, 83–77. He was named to the Third-team All-Atlantic 10 Conference as a junior. He averaged 18.5 points per game, which was fourth in the conference. In addition, Mobley led the NCAA Division I in minutes per game with 38.3. On January 31, 2018, Mobley scored a career-high 35 points and had 11 rebounds to lead St. Bonaventure to a victory over George Mason, 85–69. As a senior, Mobley averaged 18.1 points, 5.0 rebounds and 2.4 assists per game. He was named to the First-team All-Atlantic 10. Mobley set a St. Bonaventure single-season record with 105 3-pointers as a senior and set an Atlantic 10 tournament record with nine 3-pointers in a victory over Richmond; along with Jaylen Adams, Mobley helped the Bonnies to a 26–8 record. After the season, he was invited to the Portsmouth Invitational Tournament. Mobley was awarded the Oscar Robertson National Player of the Week by the United States Basketball Writers Association, for the week of February 18 2018.
