Argue furiously about stake to pledge (9)
I believe the answer is:
guarantee
'to pledge' is the definition.
(guaranteeing is a kind of pledging)
'argue furiously about stake' is the wordplay.
'furiously' indicates an anagram.
'about' is an insertion indicator.
'stake' becomes 'ante' (ante is a kind of stake).
'argue' anagrammed gives 'guare'.
'guare' going around 'ante' is 'GUARANTEE'.
(Other definitions for guarantee that I've seen before include "Promising" , "Undertake" , "Warranty, pledge" , "Provide financial security for" , "Ensure" .)