Clip nails back (4)
I believe the answer is:
snip
'clip' is the definition.
(I know that clip can be written as snip)
'nails back' is the wordplay.
'nails' becomes 'pins'.
'back' says the letters should be written backwards.
'pins' reversed gives 'SNIP'.
(Other definitions for snip that I've seen before include "Something cheap or easy to do" , "Cut quickly with a scissors" , "bargain buy" , "vasectomy?" , "Cut with scissors in small strokes" .)