The scheduled and participation algorithms of Parts 4–6 share one trait: they are always doing something. The opportunistic family works on the opposite principle. A Hide and Take algorithm - sold under aggressive brand names like “Guerrilla” or “Sniper” across the industry - spends most of its life invisible, resting in dark venues or holding quantity in reserve, and surfaces only for moments worth acting on: a burst of marketable orders, then straight back into hiding.

Why This Style Exists

The approach was born in small-cap equities, where the standard tools fail structurally:

• Schedules force bad trades: A TWAP or VWAP obeys its timetable even when the spread has blown out and the book is a desert - exactly the conditions in which forced trading is most expensive.

• Participation is always late: A POV algorithm reacts to volume after it prints. In names where liquidity arrives in rare, brief episodes, reacting late means missing the episode.

The Four Trigger Types

Implementations differ, but the trigger conditions fall into four categories:

1. Price triggers. The market moves favorably past a reference level - e.g. a dip below the arrival price or a short-term band - and the algorithm takes liquidity while the discount lasts.

2. Liquidity triggers. The book suddenly improves: an unusually tight spread, unusual depth stacked at the touch, or a large resting order appearing on the far side.

3. Manufactured opportunities. In very thin names, the algorithm can nudge the market itself: a few small marketable orders shift the price slightly, tempting counterparties to step in; the algorithm then trades against that induced flow and withdraws while the market settles.

4. Dark block discovery. The algorithm hunts size in dark pools, where a large match executes at the midpoint with no pre-trade footprint (mechanics in Part 9).

Fallback Floor

Pure opportunism has an obvious drawback: no opportunities, no fills. Most implementations therefore carry a safety layer - a minimum participation rate. If favorable moments never materialize, the algorithm quietly executes at that baseline pace, behaving like a slow POV, so the order still progresses across its horizon. The result is a hybrid: opportunistic when the market cooperates, systematic when it doesn’t.

Urgency

In practice the trader sets a single urgency parameter that tilts the whole algorithm:

• High urgency lowers the strike thresholds and raises the fallback floor - the algorithm manufactures opportunities rather than waiting for them, accepting more impact for faster completion.

• Low urgency raises the thresholds and drops the floor toward zero - the algorithm avoids marketable orders almost entirely, resting hidden at the midpoint or better and letting incoming flow cross the spread to it.

A Walkthrough

The figure above traces a buy order through a typical sequence:

1. Quiet phase. Spreads are wide, depth is thin. The algorithm posts nothing visible - hidden orders rest at the bid and midpoint. If no aggressive seller ever arrives, the market never learns the order existed.

2. Strike. A seller posts meaningful size at an attractive price, pinching the spread. The algorithm surfaces and consumes most - not all - of the new liquidity, then goes dark again.

3. Reload. If the seller replenishes, the algorithm strikes again; each round-trip captures liquidity while revealing as little as possible. If nothing reloads, it simply resumes waiting.

Risks and Etiquette

Opportunistic execution has its own leakage surface. Repeated strikes of similar size against every liquidity event build a recognizable signature - randomized strike fractions and cool-down periods help. Manufactured opportunities can be bait for predators who detect the nudge pattern and reload liquidity at worsening prices. And in the dark, resting size must be shielded from pinging with minimum-fill constraints, a defense covered in detail in Part 9. The child-order tactics that make each strike quiet - sizing, pricing, display - are the subject of Part 11.

So far every algorithm has managed a single order. Part 8 introduces the coordination problems that appear the moment two or more orders must trade as one strategy.