Change for stag — or old coins (6)
I believe the answer is:
groats
'old coins' is the definition.
'groats' can be an answer for 'coins' (groat is a kind of coin). I am unsure of the 'old' bit.
'change for stag or' is the wordplay.
'change for' indicates an anagram.
'stag'+'or'='stagor'
'stagor' is an anagram of 'GROATS'.
Can you help me to learn more?
(Other definitions for groats that I've seen before include "Crushed grain of various cereals" , "John's" , "Old English coins" , "old pieces?" .)