Accomplice often raced out with energy (11)
I believe the answer is:
confederate
'accomplice' is the definition.
(confederate is a kind of accomplice)
'often raced out with energy' is the wordplay.
'out with' indicates anagramming the letters (out can mean wrong or inaccurate).
'energy' becomes 'e' (physics symbol as in E=mc2).
'often'+'raced'='oftenraced'
'oftenraced' anagrammed with 'e' can make 'CONFEDERATE'.
(Other definitions for confederate that I've seen before include "Allied" , "US Civil War southerner" , "American soldier" , "Of the southern states in the US civil war" , "ordered into this American army" .)