Poor actor goes after work turning over script (5)
I believe the answer is:
ogham
'script' is the definition.
(medieval alphabet)
'poor actor goes after work turning' is the wordplay.
'poor actor' becomes 'ham' (ham can mean a bad or over-the-top actor).
'goes after' means one lot of letters go next to another.
'work' becomes 'go' (synonyms).
'turning' says the letters should be written backwards.
'go' backwards is 'og'.
'ham' after 'og' is 'OGHAM'.
'over' acts as a link.
(Other definitions for ogham that I've seen before include "Old British characters" , "Old Irish writing carved into stones" , "Old Irish alphabet of carved lines and notches" , "Old Irish alphabetical system with lines and notches in stone" , "Old Irish alphabet with letters of lines and notches" .)