Doctor imprisoned by a king out of control (4)
I believe the answer is:
amok
'out of control' is the definition.
(I've seen this before)
'doctor imprisoned by a king' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'imprisoned by' is an insertion indicator.
'king' becomes 'k'.
'a'+'k'='ak'
'mo' placed inside 'ak' is 'AMOK'.
(Other definitions for amok that I've seen before include "'Wildly, without self-control (4)'" , "Frenzied, running out of control" , "Must run it" , "going wild" , "(Run) in murderous frenzy" .)