Revolutionary husband taking place in battle (8)
I believe the answer is:
marathon
'battle' is the definition.
(Battle of Marathon, 490 BC)
'revolutionary husband taking place' is the wordplay.
'revolutionary' becomes 'marat' (French revolutionary Jean-Paul Marat).
'husband' becomes 'h' (abbreviation).
'taking place' becomes 'on' (as in a phrase like 'the event is on now').
'marat'+'h'+'on'='MARATHON'
'in' acts as a link.
(Other definitions for marathon that I've seen before include "strenuous event" , "Footrace of 26 miles 385 yards" , "Long and arduous" , "no easy task" , "Long-distance running event" .)