Wikia

"Lockhart and Snape turned to face each other and bowed; at least, Lockhart did, with much twirling of his hands, whereas Snape jerked his head irritably. Then they raised their wands like swords in front of them."

—Description.^[src]

An accepted combative position^[1] is one of many positions in formal wizard duelling that both duellists adopt after shortly bowing to each other, in order to show readiness for duel. The position consists of brandishing the wands, like swords in modern fencing. After a beat or, if preferred, on the count of three, the duellers start casting their first spells and start the duel.

Though the tradition of bowing is met, wizards who show little to no respect for each other would be more crude in their gesture, as Snape irritably jerked his head, while Harry Potter, Draco Malfoy and Lord Voldemort would barely incline their heads against their adversaries.