Prisoner under sentence causes delay (4,3)
I believe the answer is:
time-lag
'delay' is the definition.
(a time lag is a delay)
'prisoner under sentence' is the wordplay.
'prisoner' becomes 'lag' (slang term).
'under' says to put letters next to each other.
'sentence' becomes 'time' (a prison sentence).
'lag' put after 'time' is 'TIME-LAG'.
'causes' acts as a link.
(Other definitions for time-lag that I've seen before include "Gap between linked events" , "Interval between linked events" , "Delay between events" , "Period between two connected events" , "Delay, wait" .)