The odd idle pun caused a row (5,2)
I believe the answer is:
lined up
'caused a row' is the definition.
Although both the answer and definition are past participle verbs, I don't understand how they can define each other.
'the odd idle pun' is the wordplay.
'the odd' is an anagram indicator (I've seen 'the odds' mean this (letters in odd-numbered positions are used)).
'idle'+'pun'='idlepun'
'idlepun' anagrammed gives 'LINED UP'.
Can you help me to learn more?
(Other definitions for lined up that I've seen before include "Arranged" , "In a row" .)