Does Not So Fast cancel out Rebuke when targeting a defending unit?

Ruling: Not So Fast can counter Rebuke when Rebuke targets a unit on your battlefield.

Nuances:

• Not So Fast cannot counter spells that target battlefields (like Bullet Time) rather than units or gear, even if you control that battlefield
• Units affected by area effects are not the same as targets
• When Not So Fast counters a triggered ability with a cost paid on resolution (like Overzealous Fan), the cost is not paid and the effect does not happen