Valiant energy in new choir (6)
I believe the answer is:
'valiant' is the definition.
(I've seen this before)
'energy in new choir' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'in' means one lot of letters goes inside another.
'new' indicates an anagram.
'choir' anagrammed gives 'hroic'.
'e' put inside 'hroic' is 'HEROIC'.
(Other definitions for heroic that I've seen before include "Superhuman (efforts)" , "Showing extreme courage" , "Very brave and noble" , "Supremely courageous and brave" , "Undaunted" .)