Instead of giving checkmate, I gave stalemate. Why?

Question

I am a beginner, and I have just discovered this annoying stalemate. I got the definition but while playing, I ended up with a stalemate and I don't know why. Could you explain it to me?

[FEN "8/8/4K3/8/6R1/2k5/7R/1R1R4 w - - 0 1"]

I had 4 rooks that were supposed to block the king so he could not move anymore. Isn't this supposed to be checkmate?

Answer 1

No; for checkmate, the king must be in check, i.e. attacked by one of your pieces. This isn't the case in the position you posted, but if you were to move, you'd be able to force mate in two:

[FEN "8/8/4K3/8/6R1/2k5/7R/1R1R4 w - - 0 1"]

1. Rh3+ Kc2 2. Rg2#

Actually, you don't need that many rooks to checkmate. A lone king and rook will be enough; the procedure is explained in this Wikipedia article.

Answer 2

For checkmate you need to be able to capture the enemy king in the next move and your opponent must not have any way to prevent this.

Alternatively this can be defined by two rules that have to be satisfied simultaneously:

1. all escape squares of the king are taken; either blocked by pieces of the king's color or (as in your case) covered by the checkmating side
2. the king is in check (i.e. attacked) and cannot (a) capture the piece which gives check; nor (b) put a piece between the piece which gives check and the king so that the check is interrupted (this would only work for bishop, rook and queen checks)

In your case only "1" is satisfied, so it is not checkmate.

Answer 3

Stalemate and checkmate both involve the player to move having no legal moves. The difference is that, with stalemate, this player is not in check, but with checkmate, this player is in check.

You are correct that the Black king cannot move and, since Black has no other pieces, Black has no legal moves. But Black is not in check. Therefore, this is stalemate and not checkmate.

As Glorfindel has pointed out, if it was White’s turn instead of Black’s turn, it would be possible to force checkmate in two moves. That answer also pointed out that White could force checkmate with just one rook, as described in Wikipedia. This procedure is also described in Wikibooks, along with other useful endgames.

Finally, note that excessive promotion like this (you must have promoted at least two pawns to rooks) is usually discouraged, precisely because it often leads to stalemates like the one you accidentally created.