Paused to get warmed up with rest inside (9)
I believe the answer is:
hesitated
'paused' is the definition.
('hesitate' can be a synonym of 'pause')
'warmed up with rest inside' is the wordplay.
'warmed up' becomes 'heated' (I've seen this before).
'with' indicates putting letters inside.
'rest inside' becomes 'sit' (I've seen this before. I am not sure about the 'inside' bit.).
'heated' enclosing 'sit' is 'HESITATED'.
'to get' acts as a link.
(Other definitions for hesitated that I've seen before include "held back" , "Was not keen" , "was indecisive" , "Paused, wavered" , "Was reluctant" .)