Jag failing to be champion (5)

I believe the answer is:

notch

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'jag' is the definition.
(thesaurus)

'failing to be champion' is the wordplay.
'failing' becomes 'not' (I can't justify this - if you can you should give a lot more credence to this answer).
'to be champion' becomes 'ch' (I've seen this in other clues).
'not'+'ch'='NOTCH'

Can you help me to learn more?

(Other definitions for notch that I've seen before include "V-shaped nick" , "Nick - incision" , "Indentation, nick" , "Make the cut" , "Secure" .)

I've seen this clue in The Telegraph.

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