Delivery: high grade stone and heavy material (7)
I believe the answer is:
ballast
'heavy material' is the definition.
(ballast is heavy material)
'delivery high grade stone' is the wordplay.
'delivery' becomes 'ball' (delivery in cricket).
'high grade' becomes 'A' (academic grade).
'stone' becomes 'st' (abbreviation).
'ball'+'a'+'st'='BALLAST'
'and' is the link.
(Other definitions for ballast that I've seen before include "Material put into a ship to improve its stability" , "Weight to steady ship" , "Stabilising material" , "Heavy material used to stabilise a ship" , "mixture for concrete" .)