If the player presses shield at any point in Header's startup, the move will be canceled and Wii Fit Trainer will go into free fall for a short period of time. This leaves the ball bouncing in place directly next to Wii Fit Trainer, in prime position to be hit by any of her other attacks. This tech has a massive variety of uses due to the fact that the ball can be sent in virtually any direction and at several different speeds. As such, Header cancels (often abbreviated to "HC") can be used to edgeguard, cover options, create traps, set up kill confirms, or just simply create mixups and keep the opponent guessing. Although the soccer ball's physics were changed quite a bit from Smash 4 to Ultimate, the applications of Header cancels have remained more or less the same across both games (albeit slightly more effective in Ultimate). The primary downside to Header cancels is the fair amount of start-up time required to put one into action, especially since the player is completely helpless for a short period due to Header cancels causing free fall. However, this can be remedied somewhat by fast falling once in free fall.
While Header cancels are typically thought of as an offensive tool, they can also be used defensively in some cases. If the player performs a Header cancel and then holds shield with the ball bouncing harmlessly next to them, they able to punish most shielded attacks much more easily. This is because the opponent's attack will hit both Wii Fit Trainer's shield and the soccer ball, which then itself hits Wii Fit Trainer's shield. Since the ball has such a low amount of shieldstun, it negates most of the shieldstun from the opponent's original attack. In addition, hitting the ball keeps the opponent in hitlag for much longer than usual, giving Wii Fit Trainer a further frame advantage. As such, Header cancel shield is a powerful defensive option, allowing Wii Fit Trainer to easily punish almost every shielded move (as long as it isn't a shield breaking attack). This tech is especially useful in Ultimate since out of shield options are generally less potent.