Please see this question to build context. This question is to comply with community suggestions and to split up a large question into different part.
Following up on what's already stated on the main question:
Since all the tourneys we know about have featured almost exclusively anointed knights, I will assume that Knighthood is required to be part of a Tourney. (Yes I know Lyanna Stark fought in Tourney of Harrenhal despite not being a Knight but she did so by disguising as Knight of the Laughing tree. Barristan the Bold did it as a boy but he was also disguised as a mystery knight). The wiki however suggests that some tourneys are exclusively for knights like Tourney at Ashford and Tourney at lord butterwell's marriage but that decision lies with the game master and lord hosting it I suppose.
ASOIAF wiki says some tournaments are exclusive for knights. Does that mean a non-knighted person can appear in tilts if there is no such restriction? (I do recall something about Northmen from Winterfell fighting in Hand's Tourney lists but at least one of them was to be a knight, implying that he was a squire or near enough). Archery is open for all as we know, since Anguy the Marcher won archery tourney at KL.
Can a non-Knight appear in Melee? We have Thoros of Myr fighting in Melees with burning swords. Since he is not of the faith, we can assume he wasn't a knight. But was he? If Ser Jorah was knighted for his role in siege of Pyke despite being follower of the old gods, why not knight Thoros who was the first man through breach in Pyke? And then he was part of Brotherhood without Banners in which everyone was knighted (Which does not necessarily mean anything as he never rode in a tourney after he left KL on Lord Eddard's behest). Do we have any evidence supporting knighthood or lack of thereof of Thoros? Or any other example of non-Knighted person competing in a melee?