After a particularly brutal DADA lesson where he was disarmed and left vulnerable, Harry takes up martial arts to make sure that even if he doesn’t have his wand, he is still able to fight. His studies lead him to rediscovering an old wizard combat treatise on combat and dueling. The work details a forgotten dueling philosophy that caters more to muggleborns and those raised in the muggle world. It blends elements of muggle martial arts like evasion, blocking, absorbing an attack, and movement with spell casting and listing different spells that can be cast while on the move.
Showing his discovery to Hermione, the pair take to studying the treatise during their fourth year. Though their practice is limited due to also making sure that Harry survives the tournament, they still get some measure of competency with the style. Harry even finds that it helps him and Cedric survive their encounter with Voldemort.
When Dolores Umbridge takes over as the new Defense Professor, Harry suddenly finds himself leading a revival movement of old dueling styles along with teaching Defense against the Dark Arts. He also finds himself looking forward more and more to the sparring sessions between himself and Hermione.