Worker on a warning has a stroke (8)
I believe the answer is:
forehand
'a stroke' is the definition.
(forehand is a kind of stroke)
'worker on a warning' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'on' says to put letters next to each other.
'a warning' becomes 'fore' (I've seen this before).
'hand' put after 'fore' is 'FOREHAND'.
'has' is the link.
(Other definitions for forehand that I've seen before include "shot" , "Style of tennis stroke" , "Court action" .)