Potty at Balmoral perhaps causes rash (6)
I believe the answer is:
madcap
'rash' is the definition.
(I know that rash can be written as madcap)
'potty at balmoral perhaps' is the wordplay.
'potty' becomes 'mad' (potty can informally mean mad).
'at' means one lot of letters go next to another.
'balmoral perhaps' becomes 'cap' (balmoral is a kind of cap).
'mad'+'cap'='MADCAP'
'causes' acts as a link.
(Other definitions for madcap that I've seen before include "Foolhardy" , "Foolish, reckless" , "Impetuous irresponsible person" , "Hare-brained" , "Given to reckless behaviour" .)