Taking that as a signal, Tidus readies his own posture, is easy-going expression still there, but gaining an edge as he gets serious.

And he doesn't mind going in first with a punch from the left - a punch that pretends to be, but Tidus is quick to withdraw as he comes out with his right instead, aiming it for a shoulder, as if it's a test.

It is, in a way. Tidus's asset is his speed, if not being long-experienced.