Key bets lost, causing obligations (5)
I believe the answer is:
debts
'obligations' is the definition.
('debt' can be a synonym of 'obligation')
'key bets lost' is the wordplay.
'key' becomes 'd' (musical key).
'lost' indicates an anagram.
'bets' is an anagram of 'ebts'.
'd'+'ebts'='DEBTS'
'causing' acts as a link.
(Other definitions for debts that I've seen before include "They're owed" , "Financial obligations" , "Outstanding sums" , "Monies owed" , "Liabilities" .)