to put someone on the spot: meaning and explanation
When you put someone on the spot, you ask them a difficult question or require them to make an important decision without giving them any preparation time or warning. This causes them stress or embarrassment.
This idiom tends to be used when describing a time when this happened to you or someone you know.
It could also be used to describe someone who tends to do this to people, e.g. Just to warn you, she does like to put people on the spot.
Another useful way to use this idiom is when you are about to put someone on the spot. You can use this idiom as part of the introduction to your question or request, e.g. Sorry to put you on the spot like this, but…
Have a go at these micro-dictation exercises to hear this expression being used in context – how much can you understand?
About the sentence
…not a ballpark guess…
You can find an exercise to practise this expression here.