Enemy captures leaders of soldiers storming ditch (5)
I believe the answer is:
fosse
'ditch' is the definition.
(type of trench used in archaeology)
'enemy captures leaders of soldiers storming' is the wordplay.
'enemy' becomes 'foe' (synonyms).
'captures' is an insertion indicator.
'leaders of' says to take the initial letters.
The first letters of 'soldiers storming' is 'ss'.
'foe' going around 'ss' is 'FOSSE'.
(Other definitions for fosse that I've seen before include "-- Way, Roman road" , "Fortification ditch" , "Ditch or moat" , "Long narrow ditch" , "Long, narrow trench or excavation" .)