Grey area on pitch (4)
I believe the answer is:
ashy
'grey' is the definition.
(similar in meaning)
'area on pitch' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'pitch' becomes 'shy' (I've seen this before).
'a'+'shy'='ASHY'
(Other definitions for ashy that I've seen before include "Like fireplace residue" , "like Cinders" , "like a cinder track?" , "Like burnt wood or coal" , "Like, eg, volcanic dust" .)