Boasted heading off in tatters (6)
I believe the answer is:
ragged
'in tatters' is the definition.
(thesaurus)
'boasted heading off' is the wordplay.
'boasted' becomes 'bragged' ('brag' can be a synonym of 'boast').
'heading off' means to remove the first letter.
'bragged' with its first letter removed is 'RAGGED'.
(Other definitions for ragged that I've seen before include "Dagger could be tattered" , "Threadbare" , "Like worn-out clothing" , "Describes worn or torn clothes" , "ridiculed" .)