Comprehensively defeated (8)
(Other definitions for thrashed that I've seen before include "Beaten soundly" , "severely punished" , "given whitewashing" , "Beat violently" , "Beat soundly" .)
(Other definitions for trounced that I've seen before include "Defeated decisively" , "Thrashed, beat heavily" , "Not cured after receiving heavy beating" , "Beat hollow" .)