That One Attack/Tabletop Games

Examples of in  include:

Board Games

 * Various kinds of double attacks in Chess, given that you can't parry both in a single move. Be it forks, skewers, discovered attacks or whatever. Especially when the two pieces being simultaneously under attack are your king and queen. Also when your opponent manages to pin your queen with a rook or bishop.
 * The strongest attack you can give in a single move in orthodox chess is the double check. The only possible answer to it is moving the king out of both checks simultaneously.
 * To be precise, you've already screwed up your game at the moment when your opponent can actually make such a move. If you and your opponent both played flawlessly, the game should theoretically be drawn. It's only that once you see the move being performed, you come to realize that you goofed it up.
 * At least this is what typically happens among beginners. Grandmasters can see further, so they can usually (but not always) avoid these kinds of traps. However, they still have their Oh Crap moments, when they see their strategy is about to fail and any move they can make brings them into disadvantageous situations.
 * Double mills in Nine men's morris. They can quickly reduce the number of opponent pieces, because the player owning it can form a mill in every single move, typically continuing a Cycle of Hurting until the opponent's men are reduced to three, so they can "fly" and block the double mill. After that, a single little mistake from the "victim" will be enough to finally lose the match.

Card Games

 * Magic: The Gathering has a whole "restricted list" in Vintage and a "banned list" in other formats. Every last one of those could be That One Attack. Three cards even annoy the judges so much that they're banned in Vintage: Shahrazad, Chaos Orb, and Falling Star. There are other Vintage-banned cards, but they use ante, a mechanic involving changing ownership, something never done in tournaments.
 * The Yu-Gi-Oh Trading Card Game has several, but the effect of "Chaos Emperor Dragon-- Envoy of the End" takes the cake. For 1000 Life Points, the player can send every card on both sides of the field and in both players' hands to the Graveyard, inflicting 300 points of damage per card! You can see why the Chaos Dragon was quickly banned from competitive play. "Cemetery Bomb" has a similar effect, though not as devastating: It does 100 damage to your opponents' life points for every card in their Graveyard.