Two consume cereal in nautical event (4,4)
I believe the answer is:
boat race
'nautical event' is the definition.
'boat race' can be an answer for 'event' (boat race is a kind of event). I am not sure about the 'nautical' bit.
'two consume cereal' is the wordplay.
'two' becomes 'brace' (brace is a kind of two).
'consume' is an insertion indicator.
'cereal' becomes 'oat' (oat is a kind of cereal).
'brace' placed around 'oat' is 'BOAT-RACE'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for boat race that I've seen before include "Rowing contest" , "varsity match" , "Contest on the Thames" , "Oxford and Cambridge take part in one" , "sporting event" .)