Put your foot down in Rush (4,2,2)
I believe the answer is:
step on it
'rush' is the definition.
(I've seen this in another clue)
'put your foot down' is the wordplay.
I cannot really understand how this works, but
'put your foot down' could be 'step' (I've seen this in another clue) and 'step' is found in the answer.
The remaining letters 'onit' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for step on it that I've seen before include "Get a move on!" , "Hasten" , "Go faster - put foot down" , "Hurry up, put foot down on pedal" , "improve rate of advance" .)