Chap wearing plain jersey perhaps too much (4-3-3)
I believe the answer is:
over-the-top
'too much' is the definition.
'chap wearing plain jersey' is the wordplay.
'chap' becomes 'he'.
'wearing' indicates putting letters inside.
'plain' becomes 'overt' (both can mean visible or obvious).
'jersey' becomes 'top' (jersey is a type of top).
'overt'+'top'='overttop'
'he' going into 'overttop' is 'OVER-THE-TOP'.
'perhaps' is the link.
(Other definitions for over-the-top that I've seen before include "Excessively extreme" , "Theatrically excessive" , "To an exaggerated degree" .)