Opportunists writing motor sport book inspired by graffiti artists (13)
I believe the answer is:
carpetbaggers
'opportunists' is the definition.
(carpetbagger is a kind of opportunist)
'motor sport book inspired by graffiti artists' is the wordplay.
'motor' becomes 'car' (informal term for car).
'sport' becomes 'PE' (short for Physical Education).
'book' becomes 'b' (abbreviation for book).
'inspired by' means one lot of letters goes inside another (some letters breathed in or 'inspired' by others).
'graffiti artists' becomes 'taggers' (I've seen this in another clue).
'b' going into 'taggers' is 'tbaggers'.
'car'+'pe'+'tbaggers'='CARPETBAGGERS'
'writing' is the link.
(Other definitions for carpetbaggers that I've seen before include "investors?" , "Opportunists" .)