Looking angry about sailor’s delay (6)
I believe the answer is:
retard
'delay' is the definition.
(I know that delay is a more specific form of delay)
'looking angry about sailor's' is the wordplay.
'looking angry' becomes 'red' (red-faced).
'about' is an insertion indicator.
'sailor' becomes 'tar' (tar can mean a sailor).
'red' placed around 'tar' is 'RETARD'.
(Other definitions for retard that I've seen before include "Slow the progress of, delay" , "Hold back, slow progress" , "Slow down growth" , "Check" , "Detain" .)