With no match training, one-nil is about average (9)
I believe the answer is:
nonpareil
'with no match' is the definition.
'training one-nil is about average' is the wordplay.
'training' indicates anagramming the letters (to train can mean to grow something into a shape).
'is about' is an insertion indicator.
'average' becomes 'par' (I've seen this before).
'one'+'nil'='onenil'
'onenil' with letters rearranged gives 'noneil'.
'noneil' going around 'par' is 'NONPAREIL'.
(Other definitions for nonpareil that I've seen before include "ideal" , "Eminent beyond comparison" , "like none other" , "unmatched!" , "having no match" .)