Market traders may be bankrupt and right to be held in medieval punishment (12)
I believe the answer is:
stockbrokers
'market traders' is the definition.
(traders on the stock market)
'bankrupt and right to be held in medieval punishment' is the wordplay.
'bankrupt' becomes 'broke'.
'and' means one lot of letters go next to another.
'right' becomes 'r' (common abbreviation).
'to be held in' indicates putting letters inside.
'medieval punishment' becomes 'stocks' (device historically used for punishment).
'broke'+'r'='broker'
'broker' put within 'stocks' is 'STOCKBROKERS'.
'may be' is the link.
(Another definition for stockbrokers that I've seen is " City traders".)