Contemptible person (6)
'contemptible person' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for toerag that I've seen before include "Despicable person (slang)" , "O, great! (anag) -- a worthless fellow" , "contemptible sort" , "Squirt" , "Scamp" .)
(Other definitions for loser that I've seen before include "Unsuccessful person" , "Opposite of winner" , "Generally inept" , "Failed competitor" , "Defeated competitor" .)