Just a couple I don't really get: 5a Playwright penning a line to a yachtsman (7) P?I?T?R I'm sure it has something to do with pinter but I don't know what!
Secondly 17d as in scare, panicky (7) A?S?N?C Arsenic fits and is an anagram of in scare but I don't really get why else it is the answer