In a nutshell, USCF rules DO NOT allow helpmates when deciding whether the side whose flag fell is assigned a loss or a draw when his/her opponent lacks sufficient material to force mate. That leads directly to the familiar “mating material” rule we all learned as kids, which says the side with nothing but K+N or K+B (with no pawns) can never win on time. (I’m not sure how the USCF rules treat K+N+N when the side that flagged has a pawn.)

FIDE rules, on the other hand, definitely DO ALLOW helpmates when assessing a time-forfeit. That leads to many absurd outcomes, whose absurdity does not seem to bother officials in the slightest. I.e., K+B vs K+B is awarded a win on time if the B’s are opposite colors (as Paul showed above), but only a draw if the B’s are the same color (because the side who fell cannot use his own and his opponent’s same-color bishops to mate himself, no matter how hard he tries).

K+N gets only a draw (per FIDE) if the side that flagged has either a bare K, or K+Q and nothing else. But, K+N gets a win if the side that flagged has a N, a B, a R (obviously a helpmate can be constructed by using any of those pieces to obstruct its own king in a corner) — or even a Pawn…because that pawn — let’s call it a Zombie, shall we? — under the control of its enemy (Invasion of the Body Snatchers also comes to mind) can be mind-controlled to UNDERPROMOTE to a B, N, or R, any of which can then participate in checkmating its own king.

K+B, as noted above, gets a win when opponent flags while holding opposite-color B, and only a draw when opponent flags having same-color B (and no other pieces). K+B also gets a win on time vs K+N, but NOT vs K+R (here note that a N is superior to a B in this regard — K+N does win on time vs K+R, since a corner mate position can be constructed).

Hopefully, the near-universal adoption of time delay and/or time increment, will soon make the FIDE nonsense almost moot.

USCF Rules of Play

14D. Insufficient material to continue. The game is drawn when one of the following endings arises…

14D3. King and bishop vs. king and bishop. King and bishop vs. king and bishop, with both bishops on diagonals of the same color.

Do you have a cite for the USCF/FIDE rule which states that opposite colored bishops constitute sufficient mating material?

The reason I ask is that I once had an opponent try to claim a win on time with K+N against my K+N+P, arguing that it was possible for a mate to be constructed. When we looked up the rule, the language specifically excluded help-mates from consideration (no doubt because an earlier “creative” player had tried to make the same argument). I’d be surprised if the same didn’t apply to K+B vs. K+B, regardless of color.

(And this concludes another exciting edition of “Taking internet comments way too seriously.”

Well good luck to both teams.

P.S. your guys diagram is wrong, the bishops on on the wrong colors