Shamefaced characters cash out, unexpectedly, which will ruin their reputation (6)
I believe the answer is:
defame
'shamefaced characters cash out unexpectedly which will ruin' is the definition.
I can't judge whether this definition defines the answer.
'their reputation' is the wordplay.
'their' becomes 'de' (I am not sure about this - if you are sure you should believe this answer much more).
'reputation' becomes 'fame' (fame is a kind of reputation).
'de'+'fame'='DEFAME'
Can you help me to learn more?
(Other definitions for defame that I've seen before include "Run down" , "'Denigrate, slander (6)'" , "Attack someone's good name" , "libel" , "Charge falsely" .)