Tournament is big hit (5,4)
I believe the answer is:
grand slam
'tournament' is the definition.
The definition and answer can be both related to natural events as well as being singular nouns.
Maybe there's a link between them I don't understand?
'big hit' is the wordplay.
'big' becomes 'grands' (I can't justify this - if you can you should give a lot more credence to this answer).
'hit' becomes 'lam' (to 'lam' means to hit hard).
'grands'+'lam'='GRAND SLAM'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for grand slam that I've seen before include "It's extremely tricky" , "Winning every trick or match" , "big contract" , "sporting triumph" , "Winning everything" .)