If you were the arbiter: Episode 1

For some years, I was a chess arbiter. While preparing for the admission exams, I was studying all the chess rules, from the simplest ones to the more complicated ones.  In the midst of intricate  descriptions and explanations I stumbled upon a short paragraph whose essence can be paraphrased like this:

It's virtually impossible to enumerate all the situations that can occur over a chessboard! 

So much for precise guidelines...

It was suggested that in all the cases not listed in the booklet, an arbiter should use his commonsense when interpreting the rules and the situation.

Dangerous advice, but unavoidable, I thought.

I was an arbiter mostly in rapid tournaments, when some situations require not only commonsense but also the capacity of interpreting what is going on over the board. In those tournaments with dozens of games, the arbiter very rarely is near the "right" board, and you can be sure that the player shouting and asking for you is at the opposite side of the playing room!

Many years ago I had to deal with the following case. Black just played 1...Qxg7+ and his flag fell. White obviously claimed the victory.

Dear reader, do you agree? Stop reading if you want to solve the question by yourself!

To respond correctly to that question you must know what the regulations tell us about this topic. More or less: When a flag falls, the opponent can claim a victory if there exists a legal sequence of moves that leads to checkmate. The key word is LEGAL. In the given position, the only legal move White has is 2.Rxg7, that leads to a stalemate. So the game is drawn.

Imagine now to slightly modify the position moving back the Pawn to h4:

Now White is winning by playing 2.Kh5, an absurd but legal move, and then there is in fact a sequence of moves that leads to a checkmate. Paradoxical, isn't it?

If you are thinking that this case is very rare, okay, I may agree. But what about the following two cases, that are definitely more frequent?

In the first one, White played the last move and his flag fell. What's the correct result of this game?

The game is drawn. There is no legal sequence of moves that leads to checkmate; furthermore, it's impossible for Black to checkmate the opponent: with the white King in the corner, the Rook must be in the neighbour square to prevent the escape, but the Rook itself can cover the Bishop check. With a Knight instead of a Bishop, Black would be winning!

The second example involves Pawns, and the matter gets more complicated. Again, White played the last move and his flag fell:

Don't make the mistake to judge the position from a technical standpoint; White is obviously winning because Black cannot prevent the promotion at the next move, but that's not the point. A legal sequence does exist: White underpromotes to a Knight and then will be checkmated in the corner. A Bishop underpromotion wouldn't be enough because the two Bishops would be of the same colour and the mate is not possible. So Black is winning.

Welcome to the infinite possibilities of the chess universe!