Something Happened This Weekend

FWIW, I always announce in my pre-event announcements that capturing the king is an acceptable way of claiming an illegal move.

Alex Relyea

I think it is perfectly acceptable to capture the king according to the current rules.

So it would seem.

But that is compatible only with the “illegal move loses” rule. If the rule were changed to a 1-minute penalty (as I think it should be, both to align with FIDE and because it simply is more chess-like as far as I’m concerned), then capture-the-king would make no sense. In fact, it would mean that a player always has mating material, because there is always the possibility that the opponent might hang his king at any moment.

Bill Smythe

Attacking a King plus surrounding a King (mate) is not the same as capturing a King (which if it were left in check, is attacking only.) So I don’t think one can define any amount of material as mating material.