Calipari played sparingly in each of his first two seasons at UK and redshirted last season as a junior. According to Kentucky's website, he's on track to graduate in three years, so transferring elsewhere as a graduate could allow him to play immediately without having to sit a season due to NCAA rules.
John Calipari’s son, Kentucky guard Brad Calipari, has entered the NCAA transfer portal, per source— Matt Zenitz (@mzenitz) May 30, 2019
Entering the NCAA transfer portal does not preclude a return to the current school of enrollment, but it does allow him to openly explore other options and for coaches to contact him about playing at their school. If he were to leave, he'd be the third guard to transfer from the school, joining Jemarl Baker Jr. and Quade Green.
Calipari played in only 27 combined games in his first two seasons in which he averaged 2.65 minutes, 0.4 points and 0.2 rebounds per game for Kentucky.