Sweet, soft lump, goalkeeper (10)
I believe the answer is:
gobstopper
'sweet' is the definition.
(type of large sweet)
'soft lump goalkeeper' is the wordplay.
'soft lump' becomes 'gob' (eg a soft lump of phlegm).
'goalkeeper' becomes 'stopper' (someone who stops goals).
'gob'+'stopper'='GOBSTOPPER'
(Other definitions for gobstopper that I've seen before include "Large, hard spherical sweet" , "Large, hard sweet to suck" , "Big sweet" , "Hard round sweet" .)