^A "clause" is a restriction that keeps both battlers from having an advantage by using certain Pokemon, abilities, moves, and hold items in certain combinations. Example: Sleep clause- no two pokemon can be put to asleep at the same time, like dark void or two concecutive spore attacks in the same turn. This is "disruptive" to a stratagy when a certain stratagie used not able to be set up. With a "theme" like how the GL's are battling, a spacific "clause" can ruin the theme, thus making it harder for them to use certain pokies, in return limiting the amount of pokie choice to follow a specific theme.
Certain events and tourny's have clauses to keep the battles more balenced in order to keep fairness.