I believe my opponent has tried to cheat in a smart way but lichess algorithm has a blind spot?

Hi there,

I ve played few games against a player some while ago. The way of play and time management looked very very suspicious and i reported. Usually i get a feedback in a short that the system has caught it.

It is easy to catch someone if he is playing the first moves of engine in all moves of a game, which is what many people do.

But this time, i believe my opponent has tried to confuse system by occasionally giving free pieces and the random pawn opening to alter the average centipawn loss.

The pattern in all these three games are similar: He starts with seemingly bad opening. Then at some point he gives a free pieces and after i have an advantage, he plays engines first moves until the end of the game. Yes i also played badly like a drunk guy, but still the technique looks very artificial and suspicious. The change in strength is very weird. I checked his other games against other players and found same pattern (including his average centipawn loss), even against a strong GM. He pushed pawns in the opening and gave free piece to GM and then beat him twice.

Here are the games: (I kept my opponent anonymous as i dont want to accuse anyone in public)

Game 1:

lichess.org/study/Q43u7ipU/SbcrXh8Z#59

Game 2:

lichess.org/study/Q43u7ipU/fxanB1ey#47

Game 3:

lichess.org/study/Q43u7ipU/2HlNUXbF#27

So let me know what do you think?

It is bit hard to prove. I have been playing online for long time and experienced a lot, so my intuition says this is very suspicious, but i believe it is enough to confuse the anti-cheating algorithm?

He is are cheater 127%! But it is really hard to build AC algorithm. Especially in chess960. Maybe your opponent will banned after few reports. Hope this.

Anti-cheating is probably lightyears ahead of that what you might think.

See:

github.com/clarkerubber/irwin

www.reddit.com/r/chess/comments/9s9ml8/how_does_chesscom_and_lichess_deal_with_gms/e8n9uwg/

„ Instead these systems are based more on probability. Big websites have millions of games to analyse - including games with confirmed GMs to learn from. A fraud detection algorithm can consider unlimited questions like:

If black has a 3 pawn lead but lots of unguarded pieces and down a knight, how likely are they to aggressively recapture instead of defend?
If black has been playing aggressively, how likely are they to play a very difficult to calculate defensive move?
When black has 15 available moves, 10 of which are pretty good, how long will it take for black to play a move?
Black has played 20 straight GM level moves and has a strong material lead. What are the odds that black will now play an amateur blunder? A "look I'm not cheating" move?
Is black suddenly playing like a GM whenever there's one really important move?
Does black suddenly play very well mid game if they are slightly behind? How likely is a human to do that?
Is black playing hard to calculate moves just as fast as easy to calculate recaptures?“

Thanks @karpeshovdo, hope so too!

Thanks @Sarg0n for the links and the info!

Well, if they are lightyears ahead, maybe they ve gone too far away, we need them back to earth, cuz they still havent caught him ;) There is always room for improvement.

"Is black suddenly playing like a GM whenever there's one really important move?

Does black suddenly play very well mid game if they are slightly behind?

What are the odds that black will now play an amateur blunder? A "look I'm not cheating" move?" etc. (20. Bc2 giving free rook is such an obvious "look im not cheating move" and timing is funny; right after i typed him he is using probably engine, he gave free rook right away)

Exactly this was my approach and how i came to that conclusion. Comparing engine moves was not my primary argument but a supporting proof to my thesis.And i built my thesis during the game with such questions, so an engine check was only possible after the games anw.

#1 If you have a legitimate concern, the link is there in large, bold text on the "new forum topic" page. I'm considering reporting you for violating lichess.org/terms-of-service (rule 5 - harassment)... anyway, here is the link a second time:
lichess.org/report