Painful muscle contraction (5)
I believe the answer is:
cramp
'painful muscle contraction' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cramp that I've seen before include "Muscular spasm, very painful" , "Involuntary and painful contraction of a muscle" , "Painful muscle problem" , "Confine - muscular spasm" , "restraint" .)