Champion quality, cheeky thing? (8)

I believe the answer is:

backside

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'thing?' is the definition.
(I know that backside is a type of body part)

'champion quality' is the wordplay.
'champion' becomes 'back' (both can mean to endorse or support).
'quality' becomes 'side' (I can't justify this - if you can you should give a lot more credence to this answer).
'back'+'side'='BACKSIDE'

'cheeky' acts as a link.
This may not be correct. It may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for backside that I've seen before include "Buttocks" , "Rear" , "Bottom" , "Seat" , "Behind" .)

I've seen this clue in The Times.

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