Not in form? Do better (8)
I believe the answer is:
outclass
'do better' is the definition.
'not in form?' is the wordplay.
'not in' becomes 'out' ('out' is the opposite to 'in').
'form?' becomes 'class' ('class' can be a synonym of 'form'**).
'out'+'class'='OUTCLASS'
(Other definitions for outclass that I've seen before include "Be a cut above" , "Defeat easily; rank higher" , "Surpass greatly, be in a superior category" , "Win easily" , "Thrash" .)