Mess like in High Banks! (4)
I believe the answer is:
hash
'mess' is the definition.
(I've seen this before)
'like in high banks' is the wordplay.
'like' becomes 'as'.
'in' is an insertion indicator.
'banks' says to hollow out the word (remove centre letters) (the sides or banks of the word).
'high' with its middle taken out is 'hh'.
'as' placed into 'hh' is 'HASH'.
(Other definitions for hash that I've seen before include "Complete mess" , "that's smoked a lot" , "Error" , "Pot" , "Jumble or mixture for shah" .)