Basic Checkmate Patterns: Back Rank

This is a well-known checkmate pattern called "Back Rank":  the enemy King is at the edge of the board so he can't move backwards.  The pawns on the 7th rank block any forward movement.  His only legal moves are laterally.

Thus, if you can somehow get a heavy piece [Queen or Rook] to the back rank, it's checkmate.

In the above diagram, it's easy to see.

Now compare this to a more complicated position [Black just played ... Rxf6 [a Knight that was delivering check]:

The extra pawns are irrelevant and the Rook on f6 cannot help in the defense of the back rank.  After 2. Qc8+, Black either will resign or play 2. ... Qd8, which doesn't help because the Queen is undefended, so 3. Qxd8 will be checkmate.

If the Queen was on d6, she could block check with 2. ... Qf8, where she's protected by the King.  Or if the Rook were somewhere on the d file, Black could play 2. ... Rd8 because the Rook would be protected by the Queen.

These are things you need to look for.  Black's King and pawn configuration is common as it occurs after Kside castling and the Rooks have left the back rank [which is why you need to be wary of moving your Rooks off of the back rank].

If this still isn't clear, I suggest pulling out a physical board, setting up the above position, and playing through the alternatives until you've nailed it.  The next time this possibility crops up, you'll be more likely to recognize it.

As the attacker, anything you can do to get the enemy Queen or Rooks off the back rank so you can deliver check is worth considering.

For example, should Black take the "free" Queen?

Absolutely not:  if 1. ... Rxa7  2. Rb8+ Qd8  3. Rxd8#.

.

What about now?

Yes:  1. ... Rxa7  2. Rb8+ Rd8, blocking check with support from the Queen.

For a more complicated back rank example, look at 2/28's puzzle:

https://www.chess.com/daily-chess-puzzle/2024-02-28

[only subscribers can go back in time further than a week]

White exploited the back rank weakness with 2. Qd8:  if 2. ... Rxd8  3. Rxd8# [and if 2. ... Rcc8  3. Qf6+].  In this case, the King was all of the way in the corner, the pawn on h7 prevented forward movement, and the g Rook prevented ... Kg7.  Similar idea but with more ideas involved.

Happy Hunting!