Momentum ignition
†deadDeliberately trigger a rapid move (often by setting off others’ stops or trend algos) to profit from the cascade you started. Prohibited conduct; the tell is order flow that initiates rather than follows.
The idea
Reference figure. This concept is explained in prose and diagram; the interactive widgets live on the flagship pages it links to under Where this fits.
What is momentum ignition, and why is it illegal?
Momentum ignition is a sequence designed to start a price cascade the manipulator can profit from. The instigator fires aggressive orders to push the price through levels where stop-losses and momentum algorithms sit; those triggers cascade the price further; and the instigator, already positioned, exits into the move it manufactured, or pre-positions to fade the over-extension. The profit comes from others' reactions, not from any genuine view about value.
Markets contain reflexive triggers: stop-loss orders that fire when a level breaks, trend-following algorithms that buy strength and sell weakness, and human herd behaviour. An igniter exploits these by deliberately creating the initial move (knowing it will be amplified) and profiting from the amplification. The defining feature is intent to set off a cascade for profit, not the aggression itself: the instigator does not believe the price should move; it engineers the move so that others' reactions create the gain, then trades against the artificial extension.
The conduct creates a false or misleading impression of momentum and secures an artificial price by inducing others to trade. In the EU and UK, MAR Article 12(1)(a)–(b) captures orders or transactions that give false or misleading signals as to supply, demand or price, or that secure an artificial price level; Annex I lists indicators consistent with ignition: positions reversed over a short period, activity concentrated to move the price then unwound. In the US, the CEA disruptive-practices provisions and SEC §9/§10(b)/Rule 10b-5 reach conduct intended to create artificial price movement. See the market-abuse regimes for how each prohibition bites.
Where is the hard line from legitimate aggressive trading?
This is the genuinely difficult distinction, and the reason ignition is harder to prove than spoofing. Legitimate traders also move the price with aggressive orders, whether to execute size or because they hold a real directional view. The difference is whether the price move is the goal (ignition) or a by-product (legitimate). An aggressive momentum strategy that genuinely believes the move will continue, and stays with it, is legitimate even though it moves the price and may trigger stops. "Stop hunting" with no genuine view, engineered to flip and fade, is the prohibited form.
The decisive tells are whether the instigator profited from others' reactions and whether it traded against the move it caused. A clean directional trade continues in the same direction or simply finishes executing; an ignition round-trip reverses. The line is intent and the instrumental reversal, not the aggression, which is why a momentum or breakout strategy should be designed and documented as a genuine directional view. Surveillance, and your own algo controls, look at whether your activity systematically reverses into cascades it triggered; a strategy that stays with its signal does not produce that footprint.
How is the instrumental reversal detected?
Because the initial aggression is ambiguous, detection focuses on the whole episode, not the opening order. Surveillance reconstructs the account's full position path over the round-trip from the venue message log and looks for the signature MAR's indicators describe: a burst of aggressive same-side orders that ignites a cascade, followed by the instigator trading against the move within a short window, with positions that net out and a profit sourced from the over-extension.
Four signals combine. Position reversal after the cascade: the net position flips shortly after the spark. Profit from the over-extension: the P&L comes from fading the run, not from the original direction being correct. Concentration and timing: aggression concentrated to push through a known trigger level (a round number, a prior high or low, a cluster of stops). And a short holding period for the round-trip, which MAR Annex I explicitly lists as an indicator. Any single aggressive order is legitimate; the case is built from the pattern over the full round-trip plus intent evidence, increasingly flagged by machine-learning surveillance over episode-level features.
▸ Why the round-trip, not the spark, is where the explanation runs out optional
Surveillance scores the episode, not the opening order. A schematic flag fires when the position reverses sign over a short window, the inventory round-trips near flat, and the realised P&L is positive: the conjunction that a genuine directional view cannot produce:
A correct directional trade keeps the position; it does not flip and fade within milliseconds for a profit drawn from the over-extension. That is why the reversal is the point at which the legitimate explanation runs out, and why the case still rests on intent evidence (communications, the algorithm's design) on top of the pattern.
Is "stop hunting" always illegal?
No. "Stop hunting" (pushing the price to a level where stop-losses cluster) is the colloquial name for the ignition pattern, but it is only manipulation when done without a genuine view, engineered to trigger and then fade. Trading toward a level you genuinely believe is correct, even knowing stops sit there, is legitimate. The prohibited version is defined by the instrumental reversal, not by awareness that stops exist.
This is why a momentum or breakout strategy must be a genuine directional strategy in design and in documentation. A clean strategy that stays with its signal does not systematically reverse into cascades it triggered; a "fire to trigger, then fade" loop does, and that loop is exactly the footprint the metrics above are built to read. The awareness of stops is not the offence; the instrumental round-trip against the move you caused is.
Worked example
A synthetic, checkable detection walkthrough, as of 2026, framed as a surveillance reconstruction, how it is caught, not how it is done. A cluster of stop-loss sell orders is known to sit just below 100.00, a round number and a prior low. An account fires aggressive sells, pushing the price from 100.05 down through 100.00. The break triggers the resting stops and momentum-follower sells, and the price cascades to 99.80 within ~400 ms, far further than the instigator's own selling could explain. The instigator, which had pre-positioned to buy, now buys back into the cascade around 99.82–99.85, as the price reverts to ~99.95.
Read the tells in order. The instrumental reversal: the account sold to ignite the move, then bought against it within ~400 ms, a round-trip that nets near flat in inventory. The profit source: the gain comes from fading the over-extension the cascade produced, not from the price genuinely falling. The trigger targeting: the aggression was concentrated to break a known stop cluster at a round number. And the cascade correlation: the bulk of the move was others' triggered flow, following the spark, and the instigator's own selling could not have reached 99.80 alone.
The lesson the numbers teach: ignition is caught not at the moment of aggression but across the whole round-trip: the reversal into the cascade is where the legitimate explanation runs out. Any single aggressive sell is legitimate; the spark → cascade → reverse-and-profit signature is what opens a case, proven with the position record and intent evidence. The figures are synthetic and illustrative; a real case rests on the message and position record, not on round numbers. See market manipulation for where this sits among the related conduct.