Row caused by pair swallowing a bit of porridge (4,4)
I believe the answer is:
boat race
'row' is the definition.
(I've seen this before)
'pair swallowing a bit of porridge' is the wordplay.
'pair' becomes 'brace' (synonyms).
'swallowing' is an insertion indicator.
'a bit of porridge' becomes 'oat' (I can't justify this - if you can you should believe this answer much more).
'brace' going around 'oat' is 'BOAT-RACE'.
'caused by' acts as a link.
Can you help me to learn more?
(Other definitions for boat race that I've seen before include "televised row, perhaps" , "Cockney has to face" , "Oxford and Cambridge take part in one" , "crafty contest" , "Putney-Mortlake event" .)