Involuntary movement seen in joystick (3)
I believe the answer is:
tic
'involuntary movement' is the definition.
(I've seen this in another clue)
'in joystick' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TIC' is hidden in the letters of 'joystick'.
'seen' acts as a link.
(Other definitions for tic that I've seen before include "Nervous spasm" , "Nervous habit" , "Localised habitual twitch, especially to the face" , "Nervous movement" , "Twitch in analytical way" .)