I was thinking about what the maximum number of queens can be on the board after only legal moves. The theoretical upper bound would be 18, the original 2 queens plus 16 promoted pawns.
However, to have the pawns get past each other they would have to capture the opponent’s pieces. But they could not capture the opponents king or queen, so thats 2 less for each side (although a capture on one side would open for the other-so gets a bit tricker than that I realize). If so that would be 14, but with that many queens it would be easy to put the opponents king in check or checkmate I guess.
Is it possible to get 14 queens on the board in a legal game, and if not what is the maximum?