On the spot
Definition 1 of 3
Pro Tip 1/3Quick Decisions
Used when someone makes a decision without needing time to think. 
After seeing the performance, she offered him the job on the spot.
Pro Tip 2/3Immediate Action
Implies urgent action taken at the moment, without delay. 
The officer asked him to leave the area and he complied on the spot.
Pro Tip 3/3Surprising Outcome
Reflects a surprising or unexpected action taken immediately. 
She won the award and had to give a speech on the spot.