Draw ace quartet, ignoring the odds: about 50:50 (6)
I believe the answer is:
allure
'draw' is the definition.
(I've seen this in another clue)
'ace quartet ignoring the odds about 5050' is the wordplay.
'ace' becomes 'a' (abbreviation).
'ignoring the odds' means one should take alternating letters (letters in odd-numbered positions are removed).
'about' says to put letters next to each other.
'5050' becomes 'LL' (two Ls, Roman numerals for 50).
The alternate letters of 'quartet' are 'ure'.
'ure' after 'll' is 'llure'.
'a'+'llure'='ALLURE'
(Other definitions for allure that I've seen before include "Laurel (anag)" , "Charm, magnetism" , "Power to attract by personal charm" , "Attraction, appeal" , "Glamorous appeal" .)