Sentence is overturned leading to discharge (4)
I believe the answer is:
emit
'discharge' is the definition.
(emitting is a kind of discharging)
'sentence is overturned' is the wordplay.
'sentence' becomes 'time' (I've seen this before).
'is overturned' shows that the letters should be reversed in order.
'time' back-to-front is 'EMIT'.
'leading to' acts as a link.
(Other definitions for emit that I've seen before include "'Give off, odour say (4)'" , "Make audible sounds" , "Produce and discharge" , "Exhale" , "Expel" .)