Cut legs up (4)
I believe the answer is:
snip
'cut' is the definition.
(snip is a kind of cut)
'legs up' is the wordplay.
'legs' becomes 'pins' (pin is a kind of leg).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'pins' backwards is 'SNIP'.
(Other definitions for snip that I've seen before include "Cut - price bargain" , "nick)" , "Cut with scissors - bargain" , "Bargain (informal)" , "Cut; bargain (colloq.)" .)