Trailblazer needs one in support (7)
I believe the answer is:
pioneer
'trailblazer' is the definition.
(thesaurus)
'one in support' is the wordplay.
'in' indicates putting letters inside.
'support' becomes 'pier' (pier is a kind of support).
'one' going inside 'pier' is 'PIONEER'.
'needs' acts as a link.
(Other definitions for pioneer that I've seen before include "Ripe one (anag.)" , "make the first move!" , "Innovator; first settler" , "Innovate" , "original leader" .)