Rejected Force Select =1

[PokeChess]

Since in battles it's possible to do /showset 1 and /move 1, I think it's cool that Force Select can be "Force Select = 1". So, you can go random with team preview without choosing the lead.

 

[Lionyx]

So what's the point of team preview if not for choosing the lead? If anything, what you ask for sounds more like a clause for teams to be forcibly revealed, which sounds more intuitive in terms of name, were it to be added to PS.
It's niche enough though so agreeing beforehand on choosing the #1 Pokémon in a private challenge/room tournament seems to be the best way to go about this.

 

[DaWoblefet]

Removing Team Preview from a ruleset accomplishes this already. Including something like this in your rules will force only 1 Pokemon to be brought to the match:
!! Max Team Size = 1, !Picked Team Size, !Team Preview

What you're suggesting isn't what Force Select is for (which is for bringing a specific Pokemon, not a slot).