Long running battle (8)
I believe the answer is:
marathon
This clue could be a double definition.
'long running' is the first definition.
'Marathon' can be an answer for 'long' (thesaurus). I'm unsure of the 'running' bit.
'battle' is the second definition.
(Battle of Marathon, 490 BC)
Can you help me to learn more?
(Other definitions for marathon that I've seen before include "Race of about 26 miles" , "The longest foot race in sport" , "Olympic event" , "Long run (with a wall to get through!)" , "Race; battle" .)