Puzzle task: attack the most pieces with a single move

[Kevin Bonham]

He, he, Boris. Good one. But I have my secret weapon, I will make Kevin dizzy with 15 knights on board - think of all the knight forks! It's not every day you can claim a family check to a king and 7 knights with one single move!

That gives me an idea for a task:

What is the largest number of pieces that can become attacked with a single move?

Pieces that could have been captured as an alternative to the move are not counted. Only fresh attacks count, but this can include revealed attacks. The stupidity of the attacks is unlimited provided that the moves are legal and the position is legal (including by underpromotion).

I will open the bidding with 10 attacks:

FEN Viewer

White, to move, cannot take any piece immediately, but after 1.Nf4+ all ten black pieces are under attack.

I have only thought about this one for five minutes so maybe someone can do better.

[Kevin Bonham]

I've deleted my update posts as I have worked on this.

There is a little trick that can be used to increase the total and there are a couple of ways of using it.

With just one of the ways of using it I can increase the total to 13. With one legal move, white threatens to legally capture any of 13 black pieces, none of which white could have legally captured instead of playing that move. Even with the trick, getting 13 was rather difficult.

Using both of the ways I can increase the total to 15. (Obviously 16 is the limit because a side cannot have more than 16 pieces on the board at once.)

Without using any version of the trick I am not sure it can be increased above 10.

[Garrett]

okay if you replace the White queen with a bishop, place a black bishop on h6, the White queen on d2, the White king on c1, and Black pieces on
a2, e1, and c3 you can get to 13.

I assume that's the trick you refer to.

I am at work at the moment but when I get home I might have a go at placing the pieces to get more !

I suspect my moving everything up one rank you will be able to add black pieces on the new d1 and f1 (with the White king on the new b1).

Thanks, interesting little problem !

[Desmond]

With a different reading of the task, you could argue that both black and white pieces become attacked. Say after 1.Nf4+ the white Q and d8-R are now also attacked.

[Kevin Bonham]

Garrett, that's a different mechanism to what I had in mind again, and a neater one.

Garrett's mechanism is to pin a queen on the king. When the knight check is played, the pin is broken and the pinned piece becomes free to take pieces it would be attacking but for the pin. It is likely to be possible to get beyond 13 using this method, perhaps even to 15.

My first mechanism was to place the king itself in check but attacking pieces, so that the knight move removes the checker and unprotects pieces that the king can take:

FEN Viewer

In this position there are five pieces white would like to take with the king but can't because they are protected. However Nxe4+ unprotects three of them leaving 13 black pieces legally attacked.

My second mechanism (even dodgier) was to extend the concept by whacking a black rook on a8 and a black knight on h1. These pieces are not under attack strictly speaking because white is in check and therefore cannot take them. After taking the queen all 15 black pieces are legitimately attacked.

Not long after that I came up with this monstrosity to get 16:

FEN Viewer

White, to move, cannot take any of 14 black pieces "under attack" because he is in check and must get out of check. 1.Ng8 removes the check and attacks the remaining two pieces placing all 16 black pieces under legal attack with one move.

Neater mechanisms than this travesty are welcome.

[Alexrules01]

So once White moves, we count ALL pieces that are being attacked? i thought it was just pieces that were attacked after White moves either by the moved piece or a discovered attack from moving the piece. As I only got 10 going by a similar way that Kev did in Post #1

[Alexrules01]

Going by Kev's recent post, i think I got 16... applying to the rules... Looks a bit neater?? Lol

FEN Viewer

Ok i don't know how to create a position diagram

[Kevin Bonham]

Close but not quite! I assume your idea is to play Nf6 blocking the check and placing every black piece under attack but a problem is that the N on f6 is pinned by the black queen and therefore isn't actually legally attacking any black pieces.

My original version of my last diagram had the same problem by the way, because I tried to make it extra cute by making black able to deliver mate in 1. But in the process I pinned the white rook with a black bishop.

[Alexrules01]

Close but not quite! I assume your idea is to play Nf6 blocking the check and placing every black piece under attack but a problem is that the N on f6 is pinned by the black queen and therefore isn't actually legally attacking any black pieces.

My original version of my last diagram had the same problem by the way, because I tried to make it extra cute by making black able to deliver mate in 1. But in the process I pinned the white rook with a black bishop.

Dam! Didn't think of the pin!
Ok swapped the Knight and Queen around... looks legal now. However, Black has a mate in 1... does that make a difference?
And yes the move is Nf6!

FEN Viewer

[Kevin Bonham]

Ok swapped the Knight and Queen around... looks legal now.

Except now white is not in check and therefore has legal captures that could be made instead of playing Nf6, so some of the 16 attacks aren't new.

This is all why I came up with the idea that the attack on the checking piece could be a discovered attack, with the interposing piece taking no part except blocking. If the interposing piece makes attacks itself, then they aren't valid because the interposing piece is pinned.

[Alexrules01]

Except now white is not in check and therefore has legal captures that could be made instead of playing Nf6, so some of the 16 attacks aren't new.

This is all why I came up with the idea that the attack on the checking piece could be a discovered attack, with the interposing piece taking no part except blocking. If the interposing piece makes attacks itself, then they aren't valid because the interposing piece is pinned.

Ahh yea I get it.
very interesting idea... You got the 16, so I don't know why I'm bothering