A pre-game shitual is in fact the "ritual" of relieving one's self of inner frustrations and nervous feelings before a sporting event, in order to have a quality performance without doing the butthole dance. Usually taken in the form of a massive and satisfying dump.
John: Hey James, you coming out to the kick around before tonight's big soccer game?
James: Nah man, I have to take my pre-game shitual so I'll play to my top potential...and I had taco bell today.
John: Ah yes, it's always good to avoid the butthole dance during gametime.
James: Indeed my friend, indeed.