Why is this move not allowed?

kxg7

I assume this is a real chess rule rather than an issue with the platform... If I also imagine there's a fancy name (perhaps in French) for the rule?

Because of the pin there's no chance of the white rook on G moving anywhere and nothing else to attack my king.

Obviously kg7 puts me in check but it's not like that board couldn't have arisen from any other combination of moves...

PS I didn't lose a game like this, that screen shot came from analysis...

You can't take because you can't put your king in check. It is an illegal move, even though the rook is pinned. By rules of chess, this position would be a checkmate.

If you had some other piece that is defending that square, that would safely pick up the queen and pinned rook couldn't take it. But the king can't take as it would be in check, so Kxg7 is an illegal move.

Thanks, I thought it was a correct # result there but I was more curious about the rule itself and if there was any name or theory behind it (seems there is with almost everything in chess). I get the point of the rule that you can't have the king just sat right in front of the rook but until I saw that set up I'd never really thought about whether pins could count...

Hi! My name is Lauren Goodkind and I'm a chess coach based in California.  The white rook is protecting the white queen.  Therefore, your king cannot capture the white queen.  If the white queen wasn't protected, then your king can capture the queen.  

  Here's the bottom line: You cannot move your king into check.  

Thanks for the responses. 

I was more interested in if there was any rule or theory around pins and checks as I would have intuitively thought its only check if the piece that would take the king is actually capable of doing so (which is not the case here). It's more of a theoretical question I guess...

My point being that if kxg7 rxg7 is an impossible combination of moves (as rxg7 can't happen due to the pin) then it feels wierd to me that it'd be considered check mate, but I also understand the rules wouldn't let a king sit in front of a rook like that.

Think of it like this: "If you play the position through by taking the kings, which one is going to be taken first?". That should help contextualise why pins count

I think the thing that waa confusing me is the basic principle that the king never actually get captured, so I was thinking that if the rook can't legally move then the capture can't happen.

But I get it now... Just took a while and a few explanations to get there...  Thanks!

The pin is irrelevant, since your king would get taken first. That's why it's always illegal to move into check, because on the next move you would lose your king.

A pinned piece can deliver check. I don't think that there is a name for this phenomenon, it just follows from the rules. The important part is that even an absolutely pinned piece is considered to be attacking all squares in it's range, even if it's not able to move. It's the notion of attack which is relevant, not the actual ability to capture. Btw, note that this is the reason why it's wrong to define check as the ability to "capture the King on the next move", as many people do.

FIDE (the international body that regulates chess, Federatione Internationale d'Echecs) rule #3.9

3.9 The king is said to be 'in check' if it is attacked by one or more of the opponent's pieces,
even if such pieces are constrained from moving to that square because they would then
leave or place their own king in check. No piece can be moved that will either expose the
king of the same colour to check or leave that king in check.

This is interesting, thanks! After reading people's posts here it feels like a really clear answer, so no idea why it took so long for me to comprehend!

Better Slater than never.

The phenomenon you're thinking of is a cross-check. Try this: