Steps over the top, twirling a dagger (8)
I believe the answer is:
stiletto
'a dagger' is the definition.
(I know that stiletto is a type of dagger)
'steps over the top twirling' is the wordplay.
'steps' becomes 'stile' (set of steps in a field).
'over the top' becomes 'OTT' (abbreviation).
'twirling' is a reversal indicator.
'ott' backwards is 'tto'.
'stile'+'tto'='STILETTO'
(Other definitions for stiletto that I've seen before include "Thin high heel" , "Dagger; tapered heel" , "dangerous weapon" , "Stabbing dagger or high heel" , "Type of shoe" .)