Stunning Spell

The Stunning Spell is a charm that renders a victim unconscious and halts moving objects. It is commonly used in duels. The spell gains strength when many wizards cast it on the same target. The incantation for this spell is Stupefy. The effects may be counteracted by Ennervate, but the effects do wear off with time.

This spell may be deflected by Protego. Species known to be resistant to the spell include dragons, trolls, giants and half-giants. Rubeus Hagrid was unaffected by this spell when, in 1996, several Ministry of Magic employees attempted to remove him from Hogwarts School of Witchcraft and Wizardry grounds.

It is also possible to bewitch objects to be resistant to the spell. Fred and George Weasley bewitched their fireworks to explode when hit by Stunning Spells.

If it is used multiple times on a person, the effects can be greater. Professor McGonagall had to be moved to St. Mungo's after being hit with the spell by Ministry of Magic employees.

Etymology
"Stupefy" comes from the Latin "stupere", meaning "to be stunned."

Behind the scenes

 * In the books, it is described as a "jet of red light," but in the Harry Potter and the Order of the Phoenix (film), it's shown with a bluish-white that just knocks people off their feet.