Merrymaking in which bar gets overturned (5)
I believe the answer is:
revel
'merrymaking' is the definition.
(I know that revel is a type of merrymaking)
'bar gets overturned' is the wordplay.
'bar' becomes 'lever' (lever is a kind of bar).
'gets overturned' is a reversal indicator.
'lever' back-to-front is 'REVEL'.
'in which' acts as a link.
(Other definitions for revel that I've seen before include "Spree" , "Be festive, enjoy" , "Paint the town red" , "Riotous feast" , "Feast riotously" .)