Part of target, securing free escort (8)
I believe the answer is:
outrider
'escort' is the definition.
(I've seen this before)
'part of target securing free' is the wordplay.
'part of target' becomes 'outer' (I've seen this before).
'securing' means one lot of letters goes inside another.
'free' becomes 'rid' ('rid' can be a synonym of 'free').
'outer' enclosing 'rid' is 'OUTRIDER'.
(Other definitions for outrider that I've seen before include "As far as" , "(Motorcade) guard on motorcycle" , "Motorcade escort" .)