Tommy betrayed? That is right (7)
I believe the answer is:
soldier
'tommy' is the definition.
(Tommy can informally mean a British soldier)
'betrayed? that is right' is the wordplay.
'betrayed?' becomes 'sold' ('sell' can be a synonym of 'betray').
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'right' becomes 'r' (common abbreviation).
'sold'+'ie'+'r'='SOLDIER'
(Other definitions for soldier that I've seen before include "20 down man" , "piece of toast" , "Serve" , "Army fighter" , "One enlisted" .)