The character in question has the Curse of the Lycanthrope aspect, which causes him to become rabid and ferocious when something triggers him to transform.
The characters are all traveling together in the middle of the night, they Haven't Eaten All Day, and the Full Moon is Out.
So the GM compels the character to transform, temporarily changing the character's High Concept to Ravenous and Bloodthirsty Wolf as defined by the corresponding stunt. It is decided unanimously that the Werewolf is so hungry that it would turn on its teammates, maul them, and attempt to eat them.
Obviously there would be some out-of-character biases such as not wanting to be the player character responsible for a TPK, so is the player who controls the Werewolf allowed to concede the conflict, or do we have to wait until the compel plays out?
In other words, which rule takes precedent: the compel or the ability to concede?