What Caused This "Big Lick" Tennessee Walking Horse To Throw His Rider Asheville, NC???

This took place on Friday night, Oct. 7, 2016, in the Amateur Specialty Geldling Class at "Big Lick" North Carolina Championship Horse Show being held at the Western NC Agricultural Center in Asheville, North Carolina. (Note: This video is 3x slo mo so what happened can be closely observed).