You can also play rated correspondence chess, but unless I’m mistaken (and I’m sure someone will correct me promptly if I am), correspondence ratings are separate from over-the-board ratings. So, yeah, playing in rated tournaments is how you do it.
Don’t be scared off by the idea. It’s fun. Even if you lose all your games (which I usually do).
The only reason it’s not a flat “no” is that there are also rated matches. Taking “tournament” in its widest sense as “USCF-rated event,” the answer is no. You have to play in one (or more) such events to get a USCF over-the-board rating.
Isn’t there a restriction that you have to already have a rating before you can play in a match? So getting an initial rating has to happen at a tournament.
Well, to be completely complete, there is one other way: you could have a foreign rating or FIDE (international) rating already, and USCF could then give you an estimated USCF rating. But that means you played in tournaments or matches somewhere else to get that foreign or international rating.
We do this so that when a foreign grandmaster comes to play here, he doesn’t start off in our system as if he’s a beginner.
Where was he from, and how was he allowed to play in the Under 1600 section as an unrated? Was he assigned a rating, or were unrated players allowed to play in class sections back then? I don’t remember him even though I did the pairings for that section.
David Howell finished in a tie for 7th place in that U/1600 section, so it could be argued that he was in the right section (at least in terms of the World Open’s typical winners in under sections.)