Oddly, thugs use leek in fight (6)
I believe the answer is:
tussle
'fight' is the definition.
(tussle is a kind of fight)
'oddly thugs use leek' is the wordplay.
'oddly' means one should take alternating letters.
'thugs'+'use'+'leek'='thugsuseleek'
The alternate letters of 'thugsuseleek' are 'TUSSLE'.
'in' acts as a link.
(Other definitions for tussle that I've seen before include "Skirmish" , "Brawl" , "Fight vigorously" , "Lets us (anag) - fight" , "Grapple" .)