What the duellers did, perhaps, protected by barriers (6)
I believe the answer is:
fenced
'protected by barriers' is the definition.
'fenced' can be an answer for 'protected' (fencing is a kind of protecting). I'm unsure of the 'by barriers' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for fenced that I've seen before include "Was receiver" , "protected by barrier" , "Surrender or guarded with railings" , "Used a foil or epee" , "Recieved stolen goods" .)