Ban on-screen love (4)
I believe the answer is:
veto
'ban' is the definition.
(thesaurus)
'on-screen love' is the wordplay.
'on' means one lot of letters go next to another.
'screen' becomes 'vet' (I've seen this before).
'love' becomes 'o' (In tennis, 'love' means 'zero').
'vet' put next to 'o' is 'VETO'.
(Other definitions for veto that I've seen before include "Overrule, forbid" , "Right to reject a proposed measure" , "The right to forbid an action" , "Rule out" , "black ball" .)