Improperly takes a bet (5)
I believe the answer is:
stake
'a bet' is the definition.
('stake' can be a synonym of 'bet')
'improperly takes' is the wordplay.
'improperly' is an anagram indicator (I've seen this in other clues).
'takes' is an anagram of 'STAKE'.
(Other definitions for stake that I've seen before include "Amount bet" , "Share (in a business); post" , "Pale" , "Sharpened post; sum bet" , "Put this on horse one thinks close to winning" .)