Bill almost crazy to return (3)
I believe the answer is:
'bill' is the definition.
(a tab is a bill at a bar)
'almost crazy to return' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'crazy' becomes 'bats' (bats can informally mean crazy).
'to return' says the letters should be written backwards.
'bats' with its last letter taken away is 'bat'.
'bat' written backwards gives 'TAB'.
(Other definitions for tab that I've seen before include "Tally at bar (colloq.)" , "Check" , "Running bar bill" , "ticket" , "Bar tally; small flap" .)