Small label to stick (4)
I believe the answer is:
stab
'to stick' is the definition.
(I've seen this in another clue)
'small label' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'label' becomes 'tab' (I've seen this in another clue).
's'+'tab'='STAB'
(Other definitions for stab that I've seen before include "Attack with a knife" , "effort" , "Try - skewer" , "Pierce with pointed weapon" , "Pierce with something pointed" .)