Fire under - Idioms by The Free Dictionary
*fire under someone
Fig. something that makes someone start doing something. (*Typically: build ~; light ~; start ~.) The teacher built a fire under the students, and they really started working. You had better light a fire under your staff. Either that or we will lay off some of them.
References in classic literature
It seems that each green warrior has certain objective points for his fire under
relatively identical circumstances of warfare.
A fire under
those conditions could be extremely fast-moving,'' said Capt.
Forest Service firefighters, aided by two helicopters, brought the fire under
control in an hour.