Minor affair as pig squashes one dilapidated shed (8)
I believe the answer is:
sideshow
'minor affair' is the definition.
(a sideshow is a minor or unimportant event)
'pig squashes one dilapidated shed' is the wordplay.
'pig' becomes 'sow' (I've seen this in another clue).
'squashes' indicates putting letters inside (some letters are squashed into a word).
'one' becomes 'i' (Roman numeral).
'dilapidated' indicates an anagram.
'shed' anagrammed gives 'desh'.
'i'+'desh'='idesh'
'sow' enclosing 'idesh' is 'SIDESHOW'.
'as' is the link.
(Other definitions for sideshow that I've seen before include "Wished so for minor incident or issue - at fair?" , "Not the main scene of activity" , "affair at a fair" , "Minor display adjacent to a larger one" , "Unimportant" .)