Does threefold repetition have to be three moves in a row?

No. The three appearances can be spread across the whole game. A position from move 12 that comes back on move 30 and again on move 44 counts, as long as it is the same player to move each time and the same moves are available. Most repetitions in real games do come in a run of checks, but the rule does not require it.

Is threefold repetition automatic?

Not under Article 9.2. Somebody has to claim it, and only the player with the move can. If neither player claims, the game continues. The automatic version is Article 9.6: the fifth appearance of the same position ends the game with no claim at all, and the arbiter applies it.

What if my opponent claims a threefold that never happened?

The arbiter checks the scoresheets and rules on it. If the claim is wrong, the claimant must play the move he wrote down, and two minutes are added to your clock. That is why you write the move rather than play it: a claim that fails still has to become a legal move.

Threefold repetition rule explained

Play 1.Nf3 Nf6 2.Ng1 Ng8 3.Nf3 Nf6 4.Ng1 Ng8 and the game can be drawn on move five, with all thirty-two pieces on the board and nothing having happened at all.

The starting position, which after 1.Nf3 Nf6 2.Ng1 Ng8 3.Nf3 Nf6 4.Ng1 Ng8 has now stood on the board three times: at the start, after 2...Ng8 and after 4...Ng8. White has the move and can claim.

That is the whole rule in miniature. Three appearances of one position, same side to move, and the player to move may stop the game. Article 9.2 of the FIDE Laws is the authority.

What counts as the same position

Not “the same picture”. The Laws want the same pieces of the same colour standing on the same squares, with the same player to move and the same moves available to everybody, and that last condition quietly includes castling rights and en passant rights.

Those last two catch people out. Say your rook goes h1-g1 and later comes back to h1. The board looks identical to the position ten moves ago, but you can no longer castle kingside, so the moves available are not the same and the two positions are different. The counter starts again.

En passant works the same way. A position right after a black pawn has gone d7-d5, where your pawn on c5 may capture it in passing, is not the same position as the identical picture a few moves later when that capture has expired. Two boards, one difference you cannot see.

Making the claim

You must have the move. There are two moments, and both come before you touch anything.

If the position has just appeared for the third time and it is your turn, say so, stop the clocks and tell the arbiter. If it is about to appear because you are about to play the move that brings it back, write that move on your scoresheet, do not play it, stop the clocks and declare your intention. Either way, the claim is an offer of proof: the arbiter goes through both scoresheets.

Do not play the move first. Once the piece has landed, the position on the board is the third appearance, so if it is now your opponent’s turn, the claim is his to make and not yours. And a wrong claim is punished: you have to play the move you wrote down, and your opponent gets two minutes added to his clock. In a club game with no arbiter, you both just check the scoresheets and agree.

Where it actually turns up

Perpetual check, mostly. A queen checks on two squares, the king shuttles between two others, and after the fourth check the position has been on the board three times. Nobody plays that out to move seventy-five; somebody claims or the two players shake hands. There is a board with the checks on it on perpetual check.

The second use is quieter and worth stealing. In a sharp position, repeating once costs nothing, banks two increments on the clock, and forces your opponent to decide first whether he is playing for a win. Strong players do it constantly. Repeat twice and you have committed yourself to nothing; repeat a third time and one of you can end the game.

The rule also has a big brother that needs no claim at all: five appearances and the arbiter ends the game whether either of you wants to play on. Repeating is a defensive skill before it is a rule, and it trains like one. Defensive move puzzles are full of the moment it comes out of: the only move that holds is the one that puts the position back where it was.