He played college basketball for the Syracuse Orange. As a junior he averaged 13.0 points, 7.5 rebounds and 3.0 blocks per game, during his senior season he averaged 11.0 points, 9.6 rebounds and 3.9 blocks per game. He was rated as the #21 player in the class of 2011 by Scout.com.
He was rated as the #27 player by Rivals.com.
He was named to the Class A first team as a junior. Christmas committed to Syracuse basketball on August 6, 2010 after his junior season in high school.
He started playing for Syracuse in the 2011-2012 season. highs
Blocks: 6 against Loyola (11/25/14)
Rebounds: 16 against Hampton (11/16/14)
Points: 35 against Wake Forest (01/13/15)
On June 25, 2015, Christmas was drafted by the Minnesota Timberwolves with the 36th overall pick in the 2015 National Basketball Association draft. His rights were then traded to the Cleveland Cavaliers along with those of Cedi Osman and a future second round pick in exchange for the rights of Tyus Jones.
He later joined the Cavaliers for the 2015 National Basketball Association Summer League, where he averaged 8.0 points and 4.5 rebounds in four games.
On July 23, his rights were traded again, this time to the Indiana Pacers in exchange for a 2019 second-round pick. Four days later, he signed with the Pacers. During his rookie season, he has had multiple assignments with the Fort Wayne Mad Ants, the Pacers" Doctorate-League affiliate.
On January 29, he was named in the East All-Star team for the 2016 National Basketball Association Doctorate-League All-Star Game.