strong 1100

can a 1100 play a game at 1900 without engine ?

Add 500 to its rating to estimate the upper limit of a player's strength. If the estimate is higher than review estimate, that player is suspicious.

With longer time control, it is already very difficult and rare to win against someone with 500 points higher rating. But here, players play not so rarely much better than their rating, for example, in a rapid tournament I played, 3 players of the top 10 have now closed accounts ...

We should add that playing like 1900 and having 1900 aproximate chess.com rating in the report of a game, are two very different things, and one shouldn't base cheat detection based on it, as it is not a serious tool.

If the game was calm for instance, and there were exchanges, chess.com will easily exaggerate the aproximate rating. Along with that, in shorter games, I easily had scores far above 2 000. For instance, something forcing or almost forcing for the first 10 moves and then the opponent makes a mistake and resigns in another 5 moves.

Here is one example of what I am saying:

Realistically this wasn't the best game for the player with the black pieces. He made some logical moves for the first 10 moves, then he lost a pawn and in a bad position he lost a piece for a pawn and resigned. White simply played for the known structure, made 1 inaccurate move that could turn the game in some different direction but didn't, and just took the free stuff twice.

The report says that I played on 2 350 level, where I basically just didn't blunder in a game that gave me material twice in 25 moves. This score is a result of me having a relatively simple game. The opponent approximate rating was 1 850 which is not accurate at all, as he made 2 big mistakes that gave material away, but because he played some decent moves apart from blunders, in a somewhat known position, the report card said 1 850 in the end.

In any case, it is not a great idea to determine if someone is cheating based on this.

My spider sense was tingling , but l will accept the guy played a great game

Of course, if you let fool's mate happen, both a 100 elo and a 2000 elo would play the same thing against you.

But of course, in a long game with tactics and strategy ? Well, first, what do you define as "playing like a xxxx elo" ? Playing the same moves as an average xxxx elo would ? Well, it could just be luck. A game where by chance, repeatedy giving checks are the best moves, etc ...

But apart from that, no. If you look at 100 games played by someone in good conditions, they will give you a good estimation of their elo, and if a 100 elo "plays like a 1900" in 100 games, they should win 99 of them and climb up the rating ladder.

Also, if you are saying this because you suspect the opponent of cheating, join the Cheating Forum and make a forum there. @MGleason or other people will give you very helpful answers.

When you are suspicious, just report, and leave it to fair play team. That is the best you can do anyway.