Front running

Front running is trading ahead of a customer order to capture the price improvement that order will produce, which breaches a duty owed to that customer rather than falsifying any public price.

Also called trading ahead, anticipatory trading. Observed in equities, futures, fx, bonds, crypto. One of the related but distinct techniques. 9 enforcement actions in the library.
Updated 2026-09-07

Where is the line between front running and market manipulation?

Front running takes something from one person. Manipulation corrupts something everyone uses.

A broker who trades ahead of a customer’s large buy order captures the price improvement that customer would otherwise have received. The customer is worse off by a measurable amount. The market price, meanwhile, is exactly where genuine supply and demand put it — the large order really was coming, and it really did move the price. Nothing false was communicated to anyone.

That is why front running sits in this section. It is a breach of duty, not a falsification of the price signal.

The distinction has a practical consequence that becomes obvious in the crypto context. Strip out the duty — no broker, no customer, no relationship — and the conduct becomes legally ambiguous even though it is economically identical. That is exactly the position with sandwich attacks, and it is the clearest demonstration that the duty, rather than the trading, is what the law is addressing.

How does front running work?

1. Receive the order. A customer transmits an instruction to buy 400,000 shares. The broker now knows something the market does not: substantial buying is imminent.

2. Trade ahead. The broker buys for its own account first.

3. Execute the customer. The customer’s order pushes the price up, as large orders do.

4. Sell into it. The broker’s position is closed into the customer’s own buying.

The customer receives a worse average price than they would have without the broker’s intervention. The difference is the broker’s profit, and it comes directly out of the customer’s execution.

A worked illustration. A customer order to buy 400,000 shares in a stock quoted $18.40 bid, $18.44 offered:

The broker keeps most, though not all, of what the customer lost — the rest goes to other participants who sold into the elevated price. The customer has no way of knowing this happened unless someone compares timestamps.

What law applies?

FINRA Rule 5320 is the operative provision for most equity front running: a member firm must not trade ahead of a customer order for its own account at a price that would satisfy that order, unless it gives the customer the same price.

FINRA Rule 5270 covers block transactions specifically, prohibiting trading in a security or related instruments while in possession of material non-public information about an imminent block trade.

Rule 10b-5 reaches it as fraud, on the basis that a broker entrusted with an order implicitly represents that it will handle the order in the customer’s interest.

Best execution obligations apply independently — a broker must seek the most favourable terms reasonably available, and trading ahead is inconsistent with that by construction.

In commodities, the Commodity Exchange Act’s fraud provisions and exchange rules cover the same conduct.

What is not front running matters as much as what is. Inferring from public information that large orders are likely — index rebalances, known fund flows, predictable month-end activity — and positioning accordingly is research. The offence requires knowledge of a specific order obtained through a relationship of trust.

Which real enforcement actions have alleged front running?

This library holds 9 enforcement actions tagged front running. The table shows the largest by civil penalty together with the most recently filed. Every row links to a page carrying the regulator's own release and, where one was published, the complaint.

All 9front runningactions →

How does front running get detected?

Timestamp correlation. The core analysis, and it is definitive when the pattern exists. Compare proprietary trading timestamps against customer order receipt times across many orders. One instance is coincidence; a hundred is a practice.

Position reversal analysis. Whether the firm’s own position was closed into the customer’s execution, which is the signature that distinguishes front running from ordinary inventory management.

Information barrier review. Whether details of pending orders reached a proprietary desk, and whether the controls that were supposed to prevent it existed and functioned.

Execution quality analysis. Whether the firm’s large customer orders systematically receive worse execution than comparable orders elsewhere.

Order handling audit. Whether orders were delayed in ways that correlate with proprietary activity.

• Proprietary trades in the same instrument immediately preceding a customer order of size.
• Own-account positions that are closed into the customer's execution.
• Repetition across many customer orders, which distinguishes it from coincidence.
• Information about pending orders shared with a proprietary desk or with another firm.
• Order handling delays that correlate with proprietary activity in the same instrument.

What penalties does front running actually attract?

The numbers below are computed from this site's own case records at build time, not quoted from a secondary source. They change whenever a new action is added to the library.

What are the red flags?

• Consistently poor execution on large orders relative to smaller ones.
• Price movement in your direction beginning immediately after you transmit an order.
• A broker unwilling to explain how a block order was worked.

For an institutional client, the practical protection is measurement rather than trust: compare your execution quality across brokers, systematically, on orders of similar size and difficulty. Front running shows up as a persistent pattern in that data long before it shows up anywhere else.

Why this page exists here

Because front running is described as manipulation constantly, including by people who should distinguish them, and the difference determines which rules apply and who has been wronged.

The crypto case makes the point sharply. Sandwich attacks are economically identical to front running: someone sees a pending trade and profits by transacting around it. But there is no broker, no customer, no duty, and no confidential information — and consequently the legal position is genuinely unsettled, as the sandwich attack page sets out.

If the conduct were manipulation, the absence of a duty would not matter. That it does matter tells you which category it belongs in.

Frequently asked questions about front running

What techniques are related to front running?

• Insider trading — Insider trading is dealing in securities on material non-public information in breach of a duty of trust or confidence, which exploits a true signal others cannot see rather than injecting a false one into the price.
• Sandwich attacks and MEV — A sandwich attack places one transaction immediately before a victim's pending swap and another immediately after it, moving the pool price so that the victim trades at a worse rate and the attacker keeps the difference.
• FX fixing — FX fixing manipulation is trading during the short window used to calculate a daily currency benchmark, using advance knowledge of client orders that must be executed at that fix.
• Churning — Churning is excessive trading in a customer's account driven by the broker's commissions rather than the customer's objectives, which defrauds one identifiable person and leaves the market price untouched.

Terms defined on this page

Front Running Term · Best Execution · Order Routing · Payment For Order Flow · Maximal Extractable Value

Sources

1. FINRA Rule 5320 — prohibition against trading ahead of customer orders — FINRA
2. FINRA Rule 5270 — front running of block transactions — FINRA
3. SEC Rule 10b-5 — Electronic Code of Federal Regulations

Reviewed September 7, 2026. Every statute link points at the primary text. If something here is wrong, tell us — corrections are logged in public.