Rest in position (3)
I believe the answer is:
sit
'rest' is the definition.
(I know that rest is a more specific form of sit)
'in position' is the wordplay.
'in' indicates the answer is hidden within the clue.
'SIT' can be found hidden inside 'position'.
(Other definitions for sit that I've seen before include "Use a chair" , "Take a chair" , "Take a seat; pose" , "Model" , "Take weight off feet" .)