Drink leads to cheerful fight (5-2)
I believe the answer is:
punch-up
'fight' is the definition.
(I've seen this before)
'drink leads to cheerful' is the wordplay.
'drink' becomes 'punch' (punch is an alcoholic drink).
'leads to' says to put letters next to each other.
'cheerful' becomes 'up' (up can mean cheerful or upbeat).
'punch'+'up'='PUNCH-UP'
(Other definitions for punch-up that I've seen before include "An informal fist-fight or brawl - strike vertically?" , "Brawl (colloq.)" , "Fist fight" , "Fisticuffs incident" , "An informal fight, with vertical blows?" .)