Finished but need a hand with some of the parsing:
12A One under - second third - playwright (6) ?R?D?E I assume this is (James) BRIDIE
18D Those not in play (5) FI?L? I assume this is FILLS
18A Farm charm's clean - in Angus (6) ??R?A? I assume this is FORFAR
17D Rag, also rapping (6) ???T?O which I guess is TAT plus TOO
20D Jousting catalogues (5) L?S?S which is LISTS I assume
Any explanations will be gratefully received.