We were on display last Sunday at CCANW [ http://www.ccanw.co.uk/ ], and one of the things I thought to show the crowds was Kriegspiel - one form of chess that might count as a spectator sport. It's a sort of a cross between chess and battleships. We had a go on Tuesday night with Jeremy, Charlie and Jon.
White looking North
Umpire
Black looking South
The way it works is this:
You see your pieces, and make moves when it's your turn. You know it's your go, because you are told by the umpire that "Black has moved", and the umpire will watch you try a move. You are told by the umpire if your move is illegal ("No.") or if you should know it's illegal ("Nonsense!"). Now, pawns capture in a different way to the way they move, and you start with a lot of pawns, so it helps a lot if you know if there are any pawn captures. So, before you try a move, you are allowed to ask "Are there any pawn captures?", usually abbreviated to "Any?". The ump will reply either "No" or "You can try." ("Try."). If you successfully make a legal move, it's the turn of your opponent, and the ump will say "White has moved.". The umpire may also announce some consequences of your move:
White has moved and has captured on e5.
White has moved and Black is in check: from a Knight/along a rank or file/along a long or short diagonal
[For junior games I sometimes announce promotions.]
Got the idea?
Here are some warm-up games to see what's possible.
Game 1.
1.e4 d5
2. {"Any?" "Try."} exd5 {"White has captured on d5"} 2...Bg4 {"" i.e. no capture announced. Hmm, what else might they have done?}
3.Qxg4!
Game 2.
1.e4 d5
2. {"Any?" "Try."} exd5 {"White has captured on d5"} 2...Qxd5 {"Black has captured on d5" and now White has perfect knowledge of the position...}
3.Qg4! Qa5 {Fearing 3.Nc3, of course} 4.Qxc8# 1-0
Game 3.
1.f4 e5
2. {"Any?" "Try."} fxe5 Qh4+ {"White is in check along a short diagonal."}
3.g3 Bc5!
4. {"Any?" "Try."} Nf3 {But of course White dare not try gxh4, in case of ...Be7} 4...Qd4
5.e4 {An interesting move. White predicted ...Qe4 [idea ...Qxh1] and so played e2-e4 expecting to be told "No", when the position of the Black Queen would be known.} 5...Qf2#
0-1
Lastly, a Kriegspiel endgame task: Mate a lone Black King with Kf3 and Rh1.
Longer games are less clear, but still the spark of human intellect can be seen to run through them.
I'll put some games in the comments (I can't mix diagrams and games!)
Black looking South