"Thomas Gibson has been dismissed from Criminal Minds. Creative details for how the character's exit will be addressed in the show will be announced at a later date."
Gibson was in hot water by the show for kicking a writer on set. The physical altercation with the writer was apparently Gibson's second issue on the show. According to The Hollywood Reporter, a few years back he shoved a producer and was forced to take anger management classes.
The dismissal of Gibson from the show comes at a time when Criminal Minds was already undergoing some creative direction change. The show's former leading man, Shemar Moore left last season while they brought Paget Brewster back on. To make up for the void Gibson will leave, they have cast CSI: Miami grad Adam Rodriguez as a series regular beginning in season 12.