Mean abstainer breaks crazy odds (5)
I believe the answer is:
catty
'mean' is the definition.
(I've seen this in another clue)
'abstainer breaks crazy odds' is the wordplay.
'abstainer' becomes 'TT' (short for teetotaller, someone who avoids alcohol).
'breaks' is an insertion indicator (inserted letters break into the word).
'crazy odds' becomes 'cay' (I can't explain this - if you can you should give a lot more credence to this answer).
'tt' put into 'cay' is 'CATTY'.
Can you help me to learn more?
(Other definitions for catty that I've seen before include "Spiteful in feline way" , "It's like a queen" , "Malicious" , "Mean and spiteful" , "Backbiting" .)