Excuse the long quote from Wikipedia but there's a reason........
"
Martyn Ashton is a former British and World Champion mountain bike trials rider, stunt rider and team manager. He had been riding professional trials since 1993 and is often described as a mountain biking legend. He has been credited with turning trials from a not niche form of riding into the sport it is today. Ashton was paralysed in an accident in 2013, during a bike trials demo at the British Moto GP."
This was him at that very demo. Seconds later the day took a tragic turn.