Nowadays, revealing about stalking (9)
I believe the answer is:
shadowing
'stalking' is the definition.
(thesaurus)
'nowadays revealing about' is the wordplay.
'nowadays' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'revealing' becomes 'showing' ('show' can be a synonym of 'reveal').
'about' means one lot of letters goes inside another.
'ad' put within 'showing' is 'SHADOWING'.
(Other definitions for shadowing that I've seen before include "Trailing" , "Tailing" .)