Roby attended Dixon High School in Dixon, Illinois. He joined a team that finished its previous season with a 1–28 record, but in his final three years at Dixon, he led the team to a combined 76–13 record. In his junior season, Roby averaged 12.5 points, 9.8 rebounds, 2.6 steals and 3.7 blocks per game, earning second-team all-state Class 3A honors. As a senior, he averaged 19.7 points, 10.5 rebounds, 5.5 assists and 3.9 blocks per game. Roby finished eighth in Illinois Mr. Basketball voting and was named second-team all-state by the Chicago Sun-Times. He left Dixon with the most career rebounds and blocked in school history and the second-most career points. Roby was rated a three-star recruit by ESPN and 247Sports, and a four-star recruit by Rivals. On October 22, 2014, he committed to Nebraska.
College career
Roby entered his freshman season for Nebraska in 2016–17 with a pelvic stress reaction suffered in the offseason, delaying his college debut. He remarked, "It's probably the longest I sat out from basketball since I started playing basketball." In 30 games, Roby made four starts and averaged 3.1 points and 2.9 rebounds per game, while recording 25 blocks, the fifth-most by a Nebraska freshman. He increased his weight from to in his first year in college. As a sophomore, Roby averaged 8.7 points and team-highs of 6.3 rebounds and two blocks per game. He also led his team in field goal percentage, shooting 57 percent, and compiled 63 blocks, the most by a Nebraska player since 2001. In his junior season, Roby started in all 35 games, averaging 11.8 points, 6.9 rebounds, and 1.9 blocks per game. He led Nebraska to an unexpected run in the 2019 Big Ten Tournament. On March 30, 2019, Roby declared for the 2019 NBA draft without hiring an agent.
Professional career
He was drafted 45th by the Detroit Pistons and traded to the Dallas Mavericks. On August 7, 2019, Roby officially signed with the Mavericks. The Mavericks assigned him to the Texas Legends for the start of the NBA G League season. He suffered from plantar fasciitis which caused him to miss several games for the Legends. On January 24, Roby was traded to the Oklahoma City Thunder by the Mavericks in exchange for Justin Patton and cash considerations. He did not appear in a game during his time with the Mavericks. He made his NBA debut with a brief appearance for the Thunder in January 2020. He was then assigned shortly thereafter to the Oklahoma City Blue, returning the main Thunder roster for only a single day before being sent back to the Blue.
