Twenty orcs move with energy (5)
I believe the answer is:
score
'twenty' is the definition.
('score' can be a synonym of 'twenty')
'orcs move with energy' is the wordplay.
'move' indicates anagramming the letters.
'with' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2**).
'orcs' with letters rearranged gives 'scor'.
'scor'+'e'='SCORE'
(Other definitions for score that I've seen before include "Cut - and run!" , "Hit - music" , "Shoot a goal for a twenty" , "Twenty; scratch" , "Musical composition in written form" .)