The 9...a5 move and the Bayonet problem: a practical answer for the King's Indian

In March 2026, at an open tournament in Da Nang, I sat behind one of my students for the whole of his fourth game. He was sixteen and had spent an entire month before the event drilling the 9...Nh5 line of the King's Indian Mar del Plata. His opponent, a player nearly twenty years older, chose 9.b4 — the Bayonet. The boy followed the book correctly until move 15, then froze. Not because he had forgotten a line. He froze because the position on the board no longer resembled the position in his file: White was not striking at the centre the way he had studied, but squeezing steadily toward the queenside, and he had no plan for the queenside at all. The game ended on move 28, one pawn down and completely passive.

I once loaded the wrong SHB Da Nang tape, and from that day I knew football does not forgive carelessness. Nine years later, watching a boy freeze in front of a perfectly reasonable position, I realised chess does not forgive that kind of carelessness either. He had prepared a great deal, but he had prepared the wrong thing. He had learned moves when what he needed to learn was the position.

That is precisely why an opening product now being marketed as a "clear answer to the Bayonet" made me stop and read closely. The product recommends 9...a5, and the way it presents itself — together with what it leaves unsaid — deserves far more scrutiny than a single advertising line.

The board before anyone starts selling

The King's Indian is the classic hypermodern system: Black concedes the centre first, then strikes back with ...e5 and ...c5. The Mar del Plata variation — the name comes from the 2026 tournament — appears when White chooses the classical setup and Black answers with ...Nc6. The full move sequence of this story runs: 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 0-0 6.Be2 e5 7.0-0 Nc6 8.d5 Ne7 9.b4.

9.b4 is the Bayonet. White pushes the b-pawn, clears the way for b4-b5, prepares c5, and turns the queenside into the main battlefield. For Black this is one of the most uncomfortable challenges in the entire system: White has space and two wings to choose from, while Black must counter before being smothered. In practical play the Bayonet is White's most ambitious try in the Mar del Plata, and it has never vanished from elite tournaments — only its frequency rises and falls with fashion.

Black's main move is 9...Nh5. That is the orthodox road: the position opens up, the lines tighten, and the calculation burden explodes. A club player preparing for it has to carry an entire folder of files and still risks running into move 23 he has never seen.

The product being promoted takes a different road: 9...a5. A direct strike at the b4-pawn, the very piece White's entire plan rests on. It sounds tidy. But that tidiness has to be read through the eyes of someone who has paid for trusting a ready-made file.

What 9...a5 actually does

If White pushes b5, Black has ...a4 followed by ...c5 or ...Nc5, and the queenside changes character entirely. If White keeps b4 in place, Black has ...a4 to lock the wing and then redirect the attack. Black is not trying to seize the initiative with fire; Black is trying to break the opponent's plan before the plan takes shape.

The promotional text describes the move with familiar adjectives: sound, equal, few concrete lines, with the focus on strategy rather than tactics. Then the author himself concedes: objectively, chances are equal. In opening language that sentence means something very specific — Black has no advantage, Black has a playable position.

The real value of 9...a5 is that it changes the type of preparation work required: from calculation to judgement. That is a genuine trade, not empty marketing. For a club player, swapping forty memorised moves for ten clearly understood plans is a reasonable deal. But the deal is only reasonable if the buyer actually understands the plans, rather than buying an exemption from thinking.

In classification terms, the Bayonet family sits in ECO E97 to E99. Historically, 9...a5 is not a new invention. It is a known sideline, once used as a direct blow against the b4-pawn and the queenside. The word "answer" in the marketing is therefore relative: an answer to most players' habits, not an answer to the truth of the position.

Not a single number to verify

This is the part that bothered me most when I reread the whole document. No ACPL. No win-draw rate. No engine match rate. No game sample cited, not even a few dozen games from a public database. No named player to serve as a benchmark.

Which means every claim favourable to the product was written by the seller and is guaranteed only by the seller. Every adjective — sound, equal, few lines — in the promotional text was written by the seller, not by the data. That does not automatically make the product bad. It simply means the buyer must verify it before taking it into a real game.

Based on my experience following and recording games, a sideline only deserves trust when it has at least three things: a large enough game count, non-negative results at the target rating band, and a middlegame structure the player can actually understand. This document supplies only the third, and supplies it in words.

The most dubious line of advertising

The promotional text claims that computers do not know how to handle these positions. That claim should be discounted immediately. Modern analysis tools handle the Mar del Plata very well; it is one of the most heavily researched structures in all of chess.

What is striking is that the same author, a few paragraphs later, concedes that after 9...Nh5 computer analysis becomes important again. Two sentences in the same article contradict each other. If engines did not understand the structure, they would not become important in any branch of that structure. This is a familiar marketing trope in the opening-product genre, not a technical discovery.

The blind spot: the memoriser buying an anti-memorisation product

Few concrete lines sounds like relief. But the board does not hand out free moves. When the number of forcing lines drops, the number of decisions per move rises. In 9...Nh5 a memoriser at least has moves to recall. In 9...a5 he has to think — and thinking is exactly what he bought the product to avoid.

A memoriser who buys an anti-memorisation product will lose faster than his own self of the previous month, because in the main line he still has memory to hold on to, while in the sideline he has only unripe judgement.

In the middle of the COVID season, sitting in an empty stadium, I heard the breathing of a tactical system. In 2026, when the city locked down and matches were played without crowds, I had to read games through three fixed cameras and cross-match GPS data from eleven players. With no noise to hide behind, the structure became clearer: a young forward covered an average of 46 metres per minute inside the box yet touched the ball only 21 times. That number says nothing about whether he ran well or badly; it says the system behind him was out of rhythm. The chessboard is the same. A low-theory opening line does not tell us whether it is strong or weak; it only tells us we must read the structure rather than the list.

The transfer market resembles a king-and-pawn endgame: whoever reads the role first breathes easy. The same applies here. The value of 9...a5 lies not in the number of lines it saves but in the role it plays inside a Black repertoire. That role is to disrupt, to reclaim queenside initiative, and to drag White out of familiar preparation. It is the role of a second weapon, not of a sole weapon.

There is another risk rarely mentioned: the practical value of a sideline is cyclical. When the Bayonet becomes fashionable at elite level, the sideline gains value because White prepares for it less. When White refines the line and releases an improvement, the sideline loses value. Someone buying an opening file is buying a ticket with an expiry date, not a permanent asset.

Finally there is the question of time. The entire appeal of 9...a5 rests on the player having enough clock to think strategically. In rapid and blitz, the very quality that gives it value becomes its weakness. A queenside plan that needs three moves to unfold will be punished before it takes shape.

How to verify before the next game

With my student, I did not ban 9...a5. I set three conditions. First, re-check the line against a current database, count the games and look at Black's results at comparable rating levels — if the results are clearly negative, the promise of equality does not hold. Second, keep 9...Nh5 as a second weapon for important games, because a repertoire with a single branch is a repertoire that can be guessed. Third, study the resulting middlegame structures rather than a move list, and re-check the line each season.

The boy in Da Nang that March now has a separate page in his notebook for the queenside. That page contains no moves at all, only three questions: where is the b4-pawn going, which piece holds the wing, and which wing does Black counter on first. He has not yet won a game with 9...a5. But he has stopped freezing on move 15.

Which is perhaps the fairest measure for any opening product: not what it promises, but whether, after buying it, the player has one fewer freeze in him.