Keen on including run for a start (5)
I believe the answer is:
intro
'for a start' is the definition.
(introduction)
'keen on including run' is the wordplay.
'keen on' becomes 'into' (if you're 'into' something you're keen on it).
'including' means one lot of letters goes inside another.
'run' becomes 'r' (cricket abbreviation).
'into' placed around 'r' is 'INTRO'.
(Other definitions for intro that I've seen before include "Opening bars to a piece of popular music" , "Opening instrumental passage of song" , "Song's opening" , "this may get one started" , "Prelude" .)