The king and pawn against king endgame is a common occurrence in chess, especially in games played by beginners. I think we can safely say that it is even more common than the typical pawnless endgames – a checkmate with a queen, a checkmate with a rook, etc. It is a simple endgame, but it is by no means easy to win.
The first thing to understand about this endgame is that it is a race. The player with the pawn is trying to get it to the other side of the board to promote it to a queen, while the player with the king is trying to stop this from happening. The player with the pawn has a slight advantage because they have an extra piece on the board, but they must be careful not to overextend their pawn and leave their king vulnerable.
Let’s start with the most fundamental rule – how to recognize whether our king can catch the opponent’s pawn before it reaches the last rank to promote? It is called the rule of the square.
To apply the rule of the square, a player draws an imaginary square around the opponent’s pawn. The square has sides that are equal in length to the distance the pawn is from the promotion field. The promotion field is on the opposite side of the board from where the pawn started – the red dot in our example. See the blue crosses on the diagram above – that’s the square to follow in this strategy.
If the player’s king is inside or on the boundary of the square, it is in position to catch the opposing pawn before it promotes. If the king is outside the square, it is too far away to catch the pawn. Ergo, if it is White’s turn to move in our position, the game will finish as a draw because the white king can enter the square and follow the green trail to catch the pawn. However, in the opposite situation (Black to move), the black pawn will successfully promote, as the white king will be always one step behind it.
It is important to note that the rule of the square is a guideline and not a strict rule. It assumes that the pawns are the only pieces on the board and that there are no obstacles in the way. In practice, other pieces may be present, and the situation may be more complex. In these cases, the rule of the square may need to be adjusted or supplemented with other tactics.
To explain the previous paragraph, have a look at the most famous endgame study, created and published by Richard Réti in 1921:
Although it might look impossible at the first glance, White to move can enforce a draw. But the white king is too far away from the square, and his own pawn is dangerously close to the black king. How to resolve it? There is only one way – the white king must pursue two goals simultaneously:
- Catch the black pawn.
- Protect the white pawn.
Let’s follow Réti’s train of thought:
1. ♔g7! h4
Or 1. … ♚b6 2. ♔f6! ♚xc6 3. ♔g5 and the black pawn won’t escape.
2. ♔f6!! ♚b6 (Black sees the risk of the white king reaching its pawn, so they must use a tempo to counter it.)
If 2 … h3, then 3. ♔e7 h2 4. c7 ♚b7 5. ♔d7 and both pawns promote, so the game will be drawn.
3. ♔e5! ♚xc6 (If Black doesn’t take the pawn, the white king will get to it and ensure the promotion.)
4. ♔f4 and the white king successfully entered the square to catch the pawn.
In summary, the rule of the square is a useful concept in chess pawn endgames. It helps players determine the maximum distance their king can be from an opposing pawn to be able to catch it before it promotes. By applying this rule, players can make better decisions about how to position their pieces and increase their chances of success in these complex endgames.