Completely wrong direction (8)
I believe the answer is:
outright
'completely' is the definition.
(outright means completely or totally)
'wrong direction' is the wordplay.
'wrong' becomes 'out' (eg a calculation might be 'out').
'direction' becomes 'right' ().
'out'+'right'='OUTRIGHT'
(Other definitions for outright that I've seen before include "Total" , "Openly and frankly" , "Not qualified" , "Completely and entirely, not gradually" , "Clear" .)