Look closely at chopper sent up to pit (7)
I believe the answer is:
examine
'look closely at' is the definition.
(I've seen this before)
'chopper sent up to pit' is the wordplay.
'chopper' becomes 'axe' (something which chops).
'sent up' is a reversal indicator.
'to pit' becomes 'mine' (mining pit).
'axe' back-to-front is 'exa'.
'exa'+'mine'='EXAMINE'
(Other definitions for examine that I've seen before include "Investigate" , "Analyse" , "Inspect, peruse closely" , "Check" , "Question (a witness)" .)