Cut fasteners up (4)
I believe the answer is:
snip
'cut' is the definition.
(I know that snip is a type of cut)
'fasteners up' is the wordplay.
'fasteners' becomes 'pins' (pin is a kind of fastener).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'pins' reversed gives 'SNIP'.
(Other definitions for snip that I've seen before include "Cut; bargain (colloq.)" , "Bargain (coll)" , "Easy to do - use pins" , "Surprisingly cheap item" , "Cut back" .)