Despite that 50/50 bet, nothing! (4,2)
I believe the answer is:
even so
'despite that' is the definition.
(I've seen this in another clue)
'5050 bet nothing' is the wordplay.
'5050 bet' becomes 'evens' (evens refers to 50/50 betting odds).
'nothing' becomes 'O' (looks like zero - 0).
'evens'+'o'='EVEN SO'
(Other definitions for even so that I've seen before include "however" , "Notwithstanding" , "in any event" , "'Nevertheless (4,2)'" , "Just the same, though that may be the case" .)