Hopping mad, seeing evidence of debts attached to coat (7)
I believe the answer is:
furious
'hopping mad' is the definition.
(thesaurus)
'evidence of debts attached to coat' is the wordplay.
'evidence of debts' becomes 'IOUs' (I Owe Yous, promises to pay debts).
'attached to' means one lot of letters go next to another.
'coat' becomes 'fur' (fur coat is a kind of coat).
'ious' after 'fur' is 'FURIOUS'.
'seeing' is the link.
(Other definitions for furious that I've seen before include "Seeing red" , "how creditor feels?" , "Raging" , "Extremely angry" , "Enraged" .)