Sort of wave presented at cup match in decisive moment (10)
I believe the answer is:
tiebreaker
'sort of wave' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'at cup match in decisive moment' is the wordplay.
'at' means one lot of letters go next to another.
'cup match' becomes 'tie'.
'in decisive moment' becomes 'breaker' (I am not sure about this - if you are sure you should believe this answer much more).
'tie'+'breaker' is 'TIEBREAKER'.
'presented' acts as a link.
Can you help me to learn more?
(Other definitions for tiebreaker that I've seen before include "settler" , "It's decisive" , "Game decider" , "A means of separating equal winners" .)