Run-down vicars without energy, guts (7)
I believe the answer is:
viscera
'guts' is the definition.
(I've seen this before)
'run-down vicars without energy' is the wordplay.
'run-down' indicates an anagram (a run-down or ruined version of the letters).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'energy' becomes 'e' (physics symbol as in E=mc2).
'vicars' anagrammed gives 'viscra'.
'viscra' enclosing 'e' is 'VISCERA'.
(Other definitions for viscera that I've seen before include "organs inside" , "Internal organs, intestines" , "Entrails -- CIS rave (anag)" , "Guts" , "Abdominal organs -- cars vie (anag)" .)