Lead giant troops astray (11)
I believe the answer is:
protagonist
'lead' is the definition.
(thesaurus)
'giant troops astray' is the wordplay.
'astray' indicates anagramming the letters.
'giant'+'troops'='gianttroops'
'gianttroops' is an anagram of 'PROTAGONIST'.
(Other definitions for protagonist that I've seen before include "Leading player" , "Leading character in a play, novel, etc" , "champion" , "Lead character" , "Hero" .)