Argue crazily about bet security (9)
I believe the answer is:
guarantee
'security' is the definition.
(guarantee is a kind of security)
'argue crazily about bet' is the wordplay.
'crazily' indicates an anagram.
'about' indicates putting letters inside.
'bet' becomes 'ante' (ante is a kind of bet).
'argue' with letters rearranged gives 'guare'.
'guare' placed around 'ante' is 'GUARANTEE'.
(Other definitions for guarantee that I've seen before include "Underwrite; promise with certainty" , "Formal assurance" , "Ensure" , "Promising" , "Written assurance, pledge" .)