Grudge Training Center
Grudge Training Center was a mixed martial arts training center founded by coach Trevor Wittman in 2009. Originally located in Wheat Ridge, Colorado, GTC relocated to Arvada, Colorado in 2013. The gym was an affiliate of Jackson's Submission Fighting. Wittman closed Grudge in November 2016.Notable fighters
- Kamaru Usman – UFC welterweight champion
- Rose Namajunas – Former UFC Women's Strawweight Champion
- Nate Marquardt – UFC
- Pat Barry – UFC
- Justin Gaethje – UFC Interim Lightweight champion
- Brandon Girtz – Bellator
- Justin Salas – UFC
- Josh Copeland – UFC
- Luke Caudillo – Strikeforce, UFC
- Tyler Stinson – Bellator, Strikeforce
- Brandon Thatch – UFC
- Justin Wren – Bellator
- Shane Carwin – Former UFC Interim Heavyweight champion
- Rashad Evans – UFC Hall of Famer
- Duane Ludwig – UFC
- Ed Herman – UFC
- Todd Duffee – UFC
- Melvin Guillard – UFC
- Brendan Schaub – runner-up on
- Jon Jones – UFC Lightheavyweight Champion
- Gerald Harris – WSOF
- John Howard – UFC
- Jared Hamman – UFC
- Tyler Toner – UFC
- James McSweeney – UFC
- Paul Buentello – Bellator, Shark Fights
- Cody Donovan – UFC
- Eliot Marshall – UFC
- Alvin Robinson – UFC
;Notable and recurring trainees under Trevor Wittman
