In casino punter's raised - it's over (4)
I believe the answer is:
upon
'over' is the definition.
(thesaurus)
'in casino punter's raised' is the wordplay.
'in' indicates a hidden word.
'raised' says the letters should be written in reverse.
'nopu' is hidden within 'casino punters'.
'nopu' written backwards gives 'UPON'.
'it's' acts as a link.
(Other definitions for upon that I've seen before include "mounted" , "Abreast of, au fait with" , "In contact with" , "(Placed) on top of" , "Atop" .)