Carry out injured fencer to be given oxygen (7)
I believe the answer is:
enforce
'carry out' is the definition.
(thesaurus)
'injured fencer to be given oxygen' is the wordplay.
'injured' is an anagram indicator.
'to be given' indicates putting letters inside.
'oxygen' becomes 'o' (atomic symbol for oxygen).
'fencer' anagrammed gives 'enfrce'.
'enfrce' enclosing 'o' is 'ENFORCE'.
(Other definitions for enforce that I've seen before include "Administer with pressure (70" , "Compel or impose obedience, say to law" , "Strictly implement" , "Compel observation of" , "Impose compliance with (a law)" .)