Make a mark when you pinch (4)
I believe the answer is:
nick
This clue could be a double definition.
'make a mark' is the first definition.
(thesaurus)
'you pinch' is the second definition.
'nick' can be an answer for 'pinch' (I've seen this before). I am not certain of the 'you' bit.
'when' is the link.
Can you help me to learn more?
(Other definitions for nick that I've seen before include "Small cut - if old, the devil" , "porridge" , "Steal (informal)" , "Cop shop" , "A small indentation" .)