Just because Tidus can read this move happening doesn't make it any easier to suffer once it hits him, literally. He doesn't let go when he's tugged down, but his grip does loosen when a sharp blinding pain comes to his forehead, though, even in that instance, he's telling his hands, his fingers, not to cave. Bubbles escaping to rise with the others let out.

Sometimes, it's better to allow a temporary lose of the ball and to make a strategic move based on your skills. Such as coming up behind the person with the speed you're better at than attack or defence.

Or, when your opponent is your father, the literal face of the man you've dreamed about plummeting in a few different ways, smirking before getting a cheap shot (a cheap shot!!) on you, what you actually want to do is tangle your fingers further into the mess of his hair...

...and with pure adrenaline and spite aiding Tidus through the recoil, see how Jecht likes another one of those headbutts himself!