With the top off, left one will collapse and shatter! (4,2,6)
I believe the answer is:
fall to pieces
'shatter' is the definition.
(thesaurus)
'with the top off left one will collapse' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found within the answer.
'left' could be 'al' (I've seen this in other clues) and 'al' is present in the answer.
'one' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'and' is the link.
Can you help me to learn more?
(Another definition for fall to pieces that I've seen is " Left as police (anag) - lose emotional or mental composure".)