Mark needs regular support (4)
I believe the answer is:
spot
'mark' is the definition.
(spotting is a kind of marking)
'regular support' is the wordplay.
'regular' means one should take alternating letters.
The alternating letters of 'support' are 'SPOT'.
'needs' acts as a link.
(Other definitions for spot that I've seen before include "Difficult situation" , "See; location" , "small amount" , "moral flaw" , "Blob" .)