Dismissed just claim completely (8)
I believe the answer is:
outright
'completely' is the definition.
(outright means completely or totally)
'dismissed just claim' is the wordplay.
'dismissed' becomes 'out' (dismissed in cricket).
'just claim' becomes 'right' (as in a legal right in the justice system).
'out'+'right'='OUTRIGHT'
(Other definitions for outright that I've seen before include "Absolute - utter" , "Openly and frankly" , "Directly; without reservation" , "Completely and thoroughly" , "Altogether; openly" .)