It’s important to relieve yourself before any large event, because you never know when you’ll have an accident. Having to do a number two ruins any fun you would’ve had. In combat sports, relieving yourself beforehand is perhaps the most important thing, as this person found out.
After dieting, he realized that his bowel movements were a bit disturbed. He chose not to expel his excrement beforehand, and thought he could hold it in. What he didn’t know was that he would get choked out, which relaxed all his bodily muscles.