Fissure in the field? (5)
I believe the answer is:
gully
'fissure' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for gully that I've seen before include "Drainage channel" , "Deep ditch" , "Ravine cut by running water" , "Narrow channel - fieldsman" , "Fielding position -- narrow channel" .)