Regretting miss? Ball put over! (4)
I believe the answer is:
otis
'regretting miss?' is the definition.
(Miss Otis Regrets is a song)
'ball put over' is the wordplay.
'ball' becomes 'o' (O looks like a ball).
'put' becomes 'sit' (sitting is a kind of putting).
'over' says the letters should be written backwards.
'sit' reversed gives 'tis'.
'o'+'tis'='OTIS'
(Other definitions for otis that I've seen before include "regretful lady" , "-- Redding, US singer" , "US inventor" , "Company providing lifts" , "Lift man" .)