The 'Antidote' Claim for 9...a5: Not a Single Game Entered in the Mar del Plata Ledger

Last week I opened the promotional page of a chess opening product and carried with me the same habit that took shape at the 2026 National Premier in Ahmedabad. Back then the Gujarat State Chess Association handed me the pairings desk, not the analysis room. I logged all 216 games with Stockfish 8 at thirty seconds per move and tagged every loss above 80 centipawns against clock time. That ledger taught me the condition for using the word 'collapse': average centipawn loss must double after move thirty. This time there were no games on the counter. The page claims that in the Mar del Plata branch of the King's Indian Defence, 9...a5 is an 'antidote' to the Bayonet Attack, and that 'computers often do not know how to handle the arising complex strategic positions.' I opened the ledger. Nine information points. Not one move beyond 9.b4, not one named game, not one named player, not one engine evaluation, not one ACPL figure.

Before the verdict, let me open the ledger and count the moves.

The Mar del Plata is not a new opening. In the Classical branch of the King's Indian Defence, after 7...Nc6 you get the position in which both wings attack each other: White breaks through on the kingside with f4, g4 and h4, Black on the queenside with ...c5, ...b5 and often ...a5. The Bayonet Attack — 9.b4 — is White's space clamp: threats of b4-b5 and c4-c5, queenside room, and an obligation on Black to declare a plan. Black's standard reply has been 9...Nh5, which is forcing and therefore checkable by an engine.

Here I must repeat my evidence grades. A FIDE rating list is a measured fact. A federation press release is a reported fact. A product's promotional page is an advertising claim. These are three different grades, and merging them in one sentence is a bookkeeping error. The page I am sitting on is the third grade, and it carries words like 'often', 'complex' and 'dangerous' — not numbers.

First conclusion: this is not a refutation, it is a low-density equalising sideline. The page itself concedes that 'objectively chances are equal.' That is unusual honesty for promotional copy, and it is also the technical tell: 9...a5 is offered as a drawing tool with practical winning chances, not as an advantage-seeking weapon. For a Black player who needs a win in the last round, the tool's utility is structurally limited.

Second: the 'computers don't know' premise is dated and is doing all the marketing work. In the NNUE and neural-engine era, engines assess closed King's Indian structures far more reliably than they did in the 2000s. The defensible version of the claim is narrow: in closed positions engine evaluations are less stable and less humanly translatable — numbers hovering near equality that are hard to convert into a plan. That is a statement about usability, not about engine ignorance. The page merges the two.

Third: the 'few concrete lines, strategy over tactics' selling point is internally consistent and commercially self-undermining. A low-forcing line cannot be checked by the buyer before purchase, because there is no forcing sequence to check. Nor can it be 'refuted' afterwards. The product's central claim is therefore effectively unfalsifiable. That protects the author from criticism and lowers the product's standing with sophisticated buyers.

Fourth: there is genuine technical logic inside the 9...a5 idea. White's 9.b4 is a clamp — queenside space with the threats of b4-b5 and c4-c5. A queenside pawn move by Black strikes at the root of that clamp and steers the game away from the forcing 9...Nh5 channels into a manoeuvring fight. That is a legitimate 'avoid the machine, play the human' design. Its price is that Black accepts a permanently smaller share of the position's dynamic assets in exchange for strategic clarity. That is my external domain knowledge, not the source's claim.

Fifth: a terminology check. Calling the Bayonet Attack 'fashionable' is wrong. It is a decades-old main line, not a fashion. The label creates the impression that a new problem has arisen needing a new solution.

Sixth: 9...Nh5 is deliberately framed as the 'bad' computer-friendly path so that a contrast exists. In reality both branches live together in Black's repertoire; they are complements, not rivals.

What is missing from the ledger is also information. There is no game-database statistic in the source, no citation of an elite game. That does not mean the line is wrong; it means its practical value rests on unfamiliarity, not on objective merit. If 9...a5 were objectively promising, it would already sit closer to 9...Nh5 in elite practice. Low theoretical density usually means 'playable and so far unrefuted', not 'strong'.

The buyer picture comes out of the same ledger. The material assumes the buyer already owns a Mar del Plata repertoire, so the targeted band is an estimated 1800 to 2300 club or tournament player — an estimate, not a measured figure. The line fits classical time controls; in blitz, where pattern recall dominates, it is weak. And the 'less memorisation' pitch selects for a buyer who is sceptical of engine-driven preparation — precisely the audience least likely to demand verifiable engine data. That is coherent commercial segmentation, and it also explains the absence of data in the source.

Now I audit my own scepticism. 9...a5 is playable, so far unrefuted, and a valid practical choice for a player who does not want to memorise long variations. Low-density sidelines age slowly, so its shelf life is longer than a forcing novelty's. Absence of data does not prove the line is bad; it proves the marketing is thin. 'The claim is unsupported' and 'the claim is false' are different statements, and I will not merge them. It must also be recorded that an author who concedes 'objectively chances are equal' is more trustworthy than most promotional copy. Where the ledger closes, credit is due. The same honesty cuts the other way too: 'if Black knows what to do, things might quickly become dangerous for White' is a conditional-risk hedge that shifts the burden of proof onto the buyer's understanding. The burden of proof never sits with the buyer; it sits in the product's column.

Next time I will watch one thing: whether a named player, at a named classical event, plays 9...a5, with a date attached. The day that entry appears in a database, the claim acquires a citation. Until that day the ledger stays open — nine points, zero games, and one question every opening product should be asked: which game did your line come from?