No, you stay in. In my 1st tourney here 1200 - 1400, still ongoing, the guys that made it to the last rounds are mainly over 2000 now.
What happens after you sign up if your rating changes

But I mean, before the tourney starts. I understand your rating can climb while you are in the tourney, but what happens if your rating goes up BEFORE the tourney begins?
stwils

Unless it is an official tournament, you will stay in. (Unless the director kicks you out.) In official tournaments, you'd just get shifted to the correct category.

May I ask the reverse - what happens if when you join - your rating is within the
prescribed range but drops below the range because of a series of bad loses - I have suffered such a fate of recent weeks - sad to say - met some really tough guys one after another - with ratings far greater than my own - and was led like a lamb to the slaughter!!

Sorry to hear that. Nothing worse than getting slaughtered by folks ranked far above us.
Let's hope someone answers both our questions : rating rising or rating falling - what happens to us when the tourney actually starts?
stwils

thanks for the info, i have never entered a tournament but intend on doing so, but yesterday my rating went from 1345 down to 1165 and i have several games in play so my rating is bound to change .
i shall give a tournament a go and see what happens, thanks, mike

just tried entering a tournament to be greeted with, must have completed 5 online games to enter, oh well, paitience as they say

In my 1st tourney here 1200 - 1400, still ongoing, the guys that made it to the last rounds are mainly over 2000 now.
Yeah, it's amazing how fast some players progress. In a tournament I'm playing which started in June, some players have gained 100s of rating points since it began. I myself have gained about 250 :)
I know chess.com main tourneys say they are for certain rating players and if your rating changes before the tourney starts, you will put in another tourney. That's fine.
But what about a tourney that says it is for, say <1450 players, and you are 1400, and sign up. Then magically your rating begins to climb to about 1490 and then the tourney begins. What happens. Are you taken out?
stwils