Ham's old and green, including even bits of sauce (7)
I believe the answer is:
overact
'ham's' is the definition.
('overact' can be a synonym of 'ham')
'old and green including even bits of sauce' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'and' says to put letters next to each other.
'green' becomes 'vert' (I've seen this before**).
'including' is an insertion indicator.
'even bits of' means one should take alternating letters.
The alternate letters of 'sauce' are 'ac'.
'vert' going around 'ac' is 'veract'.
'o'+'veract'='OVERACT'
(Other definitions for overact that I've seen before include "Exaggeratedly perform a role" , "Don't expect Oscar" , "Cartoon twenty four across" , "Be unsubtle on stage" , "Perform in an exaggerated manner" .)