troops in ambush; ambush force; ambush
Military use for soldiers or a force hidden in advance to attack suddenly; it refers especially to the hidden force itself.
They placed troops in ambush on the mountain road.
The unit was attacked by enemy troops lying in ambush.
unexpected opponent; unexpected obstacle; surprise rival
Figurative use for someone or something not expected to matter but that suddenly becomes a serious rival, opposition, or obstacle.
In the election campaign, an unknown newcomer became an unexpected rival.
The unexpected obstacle in running the tournament was a sudden heavy rain.
They stationed troops in ambush behind the mountain and waited for the enemy.
The rookie turned out to be the dark horse of this tournament.
They ran into an ambush while on the march and lost many soldiers.
An unexpected dark horse appeared in the final and defeated the favorite.