That is chump catching ball (2,3)
I believe the answer is:
to wit
'that is' is the definition.
('to wit' can mean 'namely' or 'that is')
'chump catching ball' is the wordplay.
'chump' becomes 'twit' (I can't justify this - if you can you should believe this answer much more).
'catching' means one lot of letters goes inside another.
'ball' becomes 'o'.
'twit' placed around 'o' is 'TO WIT'.
Can you help me to learn more?
(Other definitions for to wit that I've seen before include "That is to say" , "i.e." , "specifically" , "what to do with a broken-down car!" , "In other words" .)