Former UFC Fighter Sean Gannon, First Man to Beat Kimbo Slice in Street Fight, Dies

Sean Gannon
Sean Gannon

Sean Gannon, a former UFC fighter who became the first man to beat the legendary Kimbo Slice in a street fight, has died.

Gannon, also a former Boston police officer, went 3-0 as an amateur and 2-0 as a pro to start his brief MMA career in the early to mid-2000s. It culminated in a lone appearance for the Ultimate Fighting Championship, a loss to Brandon Lee Hinkle at UFC 55 in 2005.

His fight with Kimbo Slice, however, is one that continues to make the rounds on social media today. At a time before Slice’s short-lived UFC, boxing, and Bellator MMA runs, Gannon fought in a grueling scrap that saw him bloodied and sporting a nasty-looking hematoma — but it was Slice who was unable to get back to his feet in the end.

Family members and Gannon’s former partner on the police force paid tribute to the former fighter on social media after news broke of his death.

“My heart is broken. I’ve lost a beloved cousin. My cousin Sean “the cannon” Gannon was best know as a former UFC fighter and former Boston Police Officer, who gained notoriety for a street fight where he was able to defeat Kimbo Slice, making him extremely famous in the fight community,” Gannon’s cousin wrote in a post to Facebook. “Less known was his brilliance – a mensa member!!; that he was like a giant loving teddy bear, one of the kindest that I know; a great father, and tenacious as hell!! He always made me feel special and God forbid anyone hurt me, he’d be my first call. He will be loved and missed Dearly. His heart was as big as his stature and his punch.”

For the better part of a decade, Gannon saw his career as a police officer restricted, after being placed on desk duty due to what the police force called a loss of cognitive function and memory issues stemming from his combat sports career. Gannon sued the city of Boston in 2012, but a superior court judge sided with the city. Gannon would appeal the ruling in 2016.

Gannon would later turn whistleblower in a series of articles on The Underground at, part of which you can read here.

No cause of death has been revealed for Gannon.