I asserted that the spell Nimue casts on Accolon cannot be found anywhere in the Advanced Dungeons & Dragons Player’s Handbook. Paul Flanaghan provides a solution.

Oh No My Sword!
(Evocation)
Level: 1?
Range: 1 jousting field.
Casting Time: When the time is right. The time will not be right for, like, hours.
Area of Effect: 1 Knight or 1 Samurai.
Frequency: Restricted
Components: S
Duration: 0
Saving Throw: None

Description: The target of the spell swings their next attack with such fury that they miss their target and lose their grip on the handle of their sword. The weapon flies 2d6 feet in a random direction (roll a d12 to determine directions with 12 being the direction the target is facing and counting around as per a clock). The target of this spell may be required, at the caster’s discretion, to shout “Oh no my sword!”, especially if the target is a Samurai.

Notes: This spell is restricted to Ladies of the Lake and unhelpful meddling wizards.