Snare wild ones crossing over at first (5)
I believe the answer is:
noose
'snare' is the definition.
('noose' can be a synonym of 'snare')
'wild ones crossing over at first' is the wordplay.
'wild' indicates an anagram.
'crossing' is an insertion indicator.
'at first' says to take the initial letters.
The first letter of 'over' is 'o'.
'ones' with letters rearranged gives 'nose'.
'nose' going around 'o' is 'NOOSE'.
(Other definitions for noose that I've seen before include "Loop for catching animals" , "A loop for the hangman" , "Loop with sliding knot in a rope" , "Hangman's knot" , "Looped rope" .)