After finishing college on a championship game run in the 2015 NCAA Tournament, Dekker was selected by the Houston Rockets with the 18th overall pick in the 2015 NBA draft.

He was one of only four true freshman to start under Bo Ryan, joining Devin Harris, Alando Tucker and Josh Gasser.

At the conclusion of the regular season, Dekker was named to the Second Team All-Big Ten by the coaches and by the media.

In the Sweet 16 against the number four seeded North Carolina Tar Heels, Dekker scored a career high 23 points and grabbed 10 rebounds to lead the 1-seed Wisconsin to a 79–72 victory.

[1][7] On July 7, he signed his rookie scale contract with the Rockets[8][9] but subsequently missed the entire 2015 NBA Summer League due to a back injury.

[17] On June 28, 2017, the Los Angeles Clippers acquired Dekker, Patrick Beverley, Montrezl Harrell, Darrun Hilliard, DeAndre Liggins, Lou Williams, Kyle Wiltjer and a 2018 first-round pick from the Houston Rockets in exchange for Chris Paul.

[20] On August 5, 2019, Dekker signed with Russian club PBC Lokomotiv Kuban of the VTB United League and the EuroCup.

[29] In the 2022-23 Eurocup season, club debut in the second european competition, they reached the play-offs but being knocked in the eightfinals against Joventut Badalona.

On November, 2024, Dekker signed a temporary contract with Joventut Badalona, a historic team from Catalonia (Spain) in the ACB League.

Joventut was also participating at the Eurocup but didn't reach the play-offs due to a bad start of the season of the Catalan team.

After being classified in 5th position for the King's Cup and his big impact on the team, Sam extended his contract until the end of the season as he became a key player since his arrival.

[33] In Summer 2012, Dekker was on the under-18 United States national team that defeated Brazil for the gold medal in the FIBA Americas championship, but his play was limited due to an injury.