Show energy during conflict (4)
I believe the answer is:
wear
'show' is the definition.
(I've seen this before)
'energy during conflict' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'during' is an insertion indicator.
'conflict' becomes 'war' (war is a kind of conflict).
'e' inserted within 'war' is 'WEAR'.
(Other definitions for wear that I've seen before include "Durability" , "display" , "North-east flower" , "Sunderland river" , "Northern river - sport" .)