Dive and jump, keeping fit inside — quite the opposite (7)
I believe the answer is:
fleapit
'opposite' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'dive and jump keeping fit inside quite' is the wordplay.
I cannot quite see how this works, but
'jump' could be 'leap' (synonyms) and 'leap' is present in the answer.
The remaining letters 'fit' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'the' is the link.
Can you help me to learn more?
(Other definitions for fleapit that I've seen before include "Scruffy cinema" , "Run-down place for pictures" , "Shabby place" , "jumper" , "Run-down cinema" .)