Upsets open containers (9)
I believe the answer is:
overturns
'upsets' is the definition.
('overturn' can be a synonym of 'upset')
'open containers' is the wordplay.
'open' becomes 'overt' ('overt' is associated in meaning with 'open').
'containers' becomes 'urns' (urn is a kind of container**).
'overt'+'urns'='OVERTURNS'
(Other definitions for overturns that I've seen before include "Upsets" , "Upends" .)