We would expect some vanishingly small fraction. Even at the grandmaster level, they happen (rarely): https://chess24.com/en/read/news/the-7-most-illegal-chess

We would expect some vanishingly small fraction. Even at the grandmaster level, they happen (rarely): https://chess24.com/en/read/news/the-7-most-illegal-chess-moves-of-all-time https://chess24.com/en/read/news/the-7-most-illegal-chess-mo...