UPDATE: MMA Fighting got statements from both Kizer and NSAC chairman Francisco Aguilar:
"It's time to move on," Kizer said in a statement, via the Las Vegas Review-Journal. "It's time to go back to being an attorney."
According to NSAC chairman Francisco Aguilar, Kizer's decision to step down was not forced, but one of his own accord. A search for Kizer's replacement is already underway.
"The board is grateful to Keith for his nearly eight years of dedicated service, which included the commission's strongest years with regard to health and safety and fiscal soundness," Aguilar said in a statement. "My fellow commissioners and I wish Keith all the best in his new role."