Strange career he led, this enthusiastic supporter (11)
I believe the answer is:
cheerleader
'enthusiastic supporter' is the definition.
(a cheerleader supports people enthusiastically)
'strange career he led' is the wordplay.
'strange' is an anagram indicator.
'career'+'he'+'led'='careerheled'
'careerheled' anagrammed gives 'CHEERLEADER'.
'this' is the link.
(Other definitions for cheerleader that I've seen before include "Dancing chanting supporter of US sports team" , "Organiser of support for a sports team" , "Enthusiastic type" , "who sounds hip?" , "Official team supporter" .)