Have you ever made an illegal move?

It was a couple of years ago in a league match for my local chess club against another chess club.
After a while we had a knight endgame on the board. We both had plenty of time on the clock.
Then my opponent played Nf4 (my king was on e2 so it was a check) and I immediately played g3.
I later went on to win that game.

After the game I sat down with a friend of mine and we analyzed the game together. During the analysis we eventually reached the abovementioned position. 1. ... Nf4+ 2. g3 and then my friend stopped me. "Uhm your king is in check you can't play g3."
At first, I couldn't believe it, but then I realize I really made an illegal move. The funny thing was, that by ignoring the check I could prevent losing material. What surprises me that both my opponent and me didn't realize that it was an illegal move. How could that happen?
Apparently, I was so confident when I played g3 so that my opponent just believed me:)

Opponent: Nf4+ check!
Me: Nope, not today! g3!
Opponent: okay

Has this ever happened to you? Have you ever witnessed people making illegal moves? Anecdotes from chess history are also welcome (looking at you Kasparov:)).

Yes I did. Once in my school chess competition, it happened but not to me. There were 5 games. In the 3rd round I was leading with all wins. Then my opponent made an illegal. I did not see it and continued. But then when I realised, I analysed it with my opponent (at the same time) and then told her about it. She did not know many rules (nor did I , cause if I did, I wouldn’t have done it) and accepted it and I later went on to go win that game by 2 illegals.

That tournament I was second and I won 4 games out of 5 on illegals!!

Thank you for seeing my story


I played chess with a long time control in a tournament with a weaker opponent. I was tired but thought I would win easily. In the opening, I castled to the long side and my opponent to the short side. I made a combination at the end of which I had to checkmate on h7 with a queen. I could not believe that my opponent does not see such simple things ...Bg5+ Qh7!#. When my opponent stopped the clock and called the judge, I didn't immediately understand what had happened, but later I saw that the bishop from g5 declares check to the king on c1. For the illegal move, they did not bet a defeat and in the end I won the game.

Yeah, in my first tournament I lost a game by illegals moves because I didn't see the checks :( I was winning the game...

The rules of OTB blitz state that an illegal move by a king forfeits the game...of course that is not possible online

In my college days a variant that was popular was OTB, 5+0, and allowed to capture the King if the opponent leaves it in check! If the King is captured the game ends. So technically leaving your King in check is not an illegal move in that variant. Your opponent might actually miss the King capture. Since one of the ideas of the variant is to get better at board vision, you really wanted to see that your King was in check. Many games ended with King captures until the person got the necessary vision. As a novice to speed chess at that time, and vision not what it needed to be, I'd miss discovered checks and get my King taken.

"Have you ever witnessed people making illegal moves?"
Yes. Novices make illegal moves OTB often. Not even talking speed chess. They leave their King in check, castle incorrectly, etc. In our club it is not unusual for novices playing each other to ask a more experienced player to watch and make sure they play a legal game.

@jomega thx for sharing your story. Integrated board vision exercises;) Seems like king safety is key in that variant.
In our youth tournament in our town we always have multiple arbiters looking at the games just in case something goes wrong. Both sides can learn from that.