Upsetter and Unknown quantity

Upsetter noun - An unexpected winner; someone who defeats the favorite competitor.

Unknown quantity and upsetter are semantically related in remote possibility topic. In some cases you can use "Unknown quantity" instead a noun "Upsetter".

Unknown quantity noun - A factor in a given situation whose bearing and importance is not apparent.

Upsetter and unknown quantity are semantically related in remote possibility topic. You can use "Upsetter" instead a noun phrase "Unknown quantity".