... studied safe reversing in training day (7)
I believe the answer is:
perused
'studied' is the definition.
(I've seen this before)
'safe reversing in training day' is the wordplay.
'safe' becomes 'sure' (I've seen this before).
'reversing' says the letters should be written backwards.
'in' is an insertion indicator.
'training' becomes 'pe'.
'day' becomes 'd'.
'sure' back-to-front is 'erus'.
'erus' going into 'pe' is 'peruse'.
'peruse'+'d'='PERUSED'
(Other definitions for perused that I've seen before include "Browsed" , "Studied" , "Read (something) very carefully" , "Scanned" .)