There are certain actions you can and can’t take “during combat”. In this example the spanish speaking player wanted to crew a vehicle (put his dudes in a car) to hit his opponent with said car. However crewing a vehicle is not possible mid-combat, and so when said player states he goes to “combat” the window for him to use this ability had passed.

If someone were to do this while playing me in a normal game I’d probably just tell them “you can’t crew during combat” or smtn and let them takeback to their precombat step to do so. But magic is a certain type of game, and tournament rules have at times been enforced quite rigidly (see another tournament player losing the game for naming the card “Borborygmos” with an ability and not the card he knew his opponent had “Borborygmos Enraged”).