14 The rule of the square
Think of a large square which is defined by the route the pawn takes to reach the promotion square. If the black king is inside that square it catches the pawn, otherwise it does not.
In the following example the black king is outside of the square. The pawn runs off and the king cannot catch it. Black loses.
Move directly on the board to input a solution. Either click first on the start square and then on the target square. Or click on the piece, hold on to it, move it tot he target square and let go of it. The button ‘Left arrow’ takes back the move.
The rule of the square allows you to know at once if a king can catch a passed pawn.