We’re not talking about Great Aunt Tessie’s brooch but the chess term relative pin.
Diagram-1: The white knight at f3 is pinned . . . or is it?
In Diagram-1, we see that the knight at f3 is under a relative pin. This means that it can legally move, but it might be foolish to move that piece, for the black bishop could then capture the white queen.
What problem could you have when you depend on a relative pin, a problem you’d never have with an absolute pin? Just as your Aunt Tessie might take off the brooch pin she had been wearing, so in chess a relative pin might be unfastened. That’s the case in the opening position shown in Diagram-1.
Who would suspect that, within two moves, the f7 square could become a weak point for black, allowing white to get a quick checkmate in this opening? Few players would suspect such a checkmate, without prior knowledge of this opening trap.
Diagram-2: White can ignore the relative pin on that knight because of a mate
Here’s the shock: White can capture the black pawn at e5 with the knight that appeared to have been pinned. Now consider why the pin failed to hold that knight down.
Diagram-3: The black bishop captured the white queen, but look deeper
The loss of the white queen was an intentional sacrifice, for now white gets checkmate in two moves: Bxf7+ (black must then move Ke7) and then Nd5# mate. We’ll look at the moves one at a time.
Diagram-4: White just captured the pawn that was on f7 (Bxf7+)
Black now has only one way to get out of that check from the bishop that’s now at f7. The black king must move to e7, for that bishop is protected by the white knight at e5. The d7 square is off limits to that king as well, because of that knight.
Diagram-5: The black king just moved to e7, the only legal move
Do you see the checkmate that is available to white in Diagram-5? That is the whole point of the queen sacrifice, for white now wins the game.
Diagram-6: White wins by checkmate with Nd5#
Notice how the black king is checkmated in Diagram-6. The white knight, that just moved to d5, puts the king in check and also covers the f6 square. The bishop covers e8 and e6. The other knight, the one at e5, covers d7 and protects that bishop. Checkmate.
This is not to say that relative pins don’t usually work. Not at all, for they usually do keep a piece confined, at least to some extent. The relative pin just failed to hold in this position.
Learn to imagine a move, looking at the board as if the move were already made
She [Susan Polgar] has been promoting chess for children for many years in the United States, a nation that actively promotes sports for the physical development of students but promotes intellectual competition (like chess) much less than European countries promote the game in schools.
Three levels of chess beginners
In chess, a pin is a situation brought on by an attacking piece in which a defending piece cannot move without exposing a more valuable defending piece on its other side . . .