Ancient lines read back, exit play without hindrance (5)
I believe the answer is:
ogham
'ancient lines' is the definition.
(Ogham was a medieval alphabet of line markings)
'back exit play without hindrance' is the wordplay.
I cannot really see how this works, but
'play' could be 'ham' (hamming is a kind of playing) and 'ham' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'read' is the link.
Can you help me to learn more?
(Other definitions for ogham that I've seen before include "Old Irish writing of carved lines and notches" , "Old Celtic alphabet" , "Old Irish alphabet of carved lines and notches" , "set of characters" , "Old British characters" .)