A 6 ft 1 in (1.85 m) point guard, he played college basketball for Loyola University Chicago, and was the 2018 Missouri Valley Conference Player of the Year.
[2] As a freshman in the 2014–15 season, Custer played sparingly behind the Cyclones' Monté Morris, one of the top point guards in the Big 12 Conference.
[2] After sitting out the 2015–16 season per National Collegiate Athletic Association (NCAA) transfer rules, Custer immediately joined the Ramblers' starting lineup, allowing star Milton Doyle to play off the ball.
[4] As a redshirt junior, Custer led the Ramblers to the Missouri Valley Conference regular-season title, despite missing five games to an ankle injury.
[11] After serving in that role for one season, Custer followed head coach Porter Moser to Oklahoma to become their Director of Video Operations & Player Development.