The sort of men that serve behind bars (9)
I believe the answer is:
convicted
'men that serve behind bars' is the definition.
I can't tell whether this definition defines the answer.
'the sort of' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'of' could be 'o' and 'o' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for convicted that I've seen before include "Declared guilty (of offence)" , "being found guilty" .)