Beat off party (5)
I believe the answer is:
outdo
'beat' is the definition.
(I know that beat is a more specific form of the action outdo)
'off party' is the wordplay.
'off' becomes 'out' (both can mean wrong or inaccurate).
'party' becomes 'do' (do is a kind of party).
'out'+'do'='OUTDO'
(Other definitions for outdo that I've seen before include "Get the better of" , "Exceed" , "Perform better than, be superior to" , "Go one beter than, surpass" , "Surpass someone at something" .)