Fruit ending in tin, on average around about fifty (5,6)
I believe the answer is:
navel orange
'fruit' is the definition.
(navel orange is a kind of fruit)
'ending in tin on average around about fifty' is the wordplay.
I cannot quite see how this works, but
'around' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'about' could be 'a' (abbreviation in Chambers) and 'a' is present in the answer.
'fifty' could be 'l' ('L' can be a synonym of 'fifty') and 'l' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for navel orange that I've seen before include "Citrus fruit" , "Large fruit" .)