Watson was a consensus five-star recruit, one of the top small forwards and the highest-ranked player from California in the 2021 recruiting class.[8] On July 27, 2020, he committed to playing college basketball for UCLA over offers from Arizona, Gonzaga, Michigan, Oregon and Washington.[9] He was frank with the Bruins coaching staff that he intended to be a one-and-done player, leaving for the NBA after one year in college.[10]
As a freshman at the University of California, Los Angeles in 2021–22, Watson arrived out of shape, primarily due to his high school senior season being disrupted by the COVID-19 pandemic.[10] He joined an experienced UCLA group that had advanced to the Final Four of the NCAA tournament a year earlier.[11] All five starters returned, and he received no guarantees about his playing time.[12] Watson's defense was more advanced than his offense. However, the Bruins had other established scorers.[11] He received honorable mention for the Pac-12 All-Freshman Team.[13] He averaged 3.3 points and 2.9 rebounds in 12.6 minutes per game, and made just 32.2% of his field goals and 22.6% of his 3-pointers. His playing time was sporadic, and he logged 10 minutes or more in just two out of the last seven games of the season.[14] After the season, Watson declared for the NBA draft, forgoing his remaining college eligibility.[15]
Watson represented the United States at the 2021 FIBA Under-19 World Cup in Latvia. He averaged four points, 3.4 rebounds and 2.7 assists per game, helping his team win the gold medal.[19]
Watson's father, Julio, is a medical device representative, and his mother is an event planner. He has a younger brother, Christian, who plays basketball at Long Beach Polytechnic High School, and a younger sister, Jolie Grace.[21]