Aggressor

Aggressor classification is per-trade, not per-order: each executed trade is tagged buy-side aggressor (a market buy lifted a resting ask) or sell-side aggressor (a market sell hit a resting bid), based on which side crossed the spread to make the trade happen. Volume gets summed by aggressor side over any window to build a running picture of buy-side versus sell-side pressure.

A stretch of trading dominated by buy-side aggressor volume, even without a large net price move yet, suggests buyers are actively working to get filled rather than simply waiting for price to come to them. That's a different posture from a market where price drifts up on thin volume with no clear aggressor lean, which looks more like an absence of sellers than a presence of eager buyers. Aggressor data is most useful compared over time and against the passive side's behavior: whether resting size is holding, thinning, or refilling as it gets hit.

Being the aggressor tells you who initiated a specific trade. It does not tell you why, or whether that trader is right. A large aggressive buy can be a stop-loss order forced to execute at market, unrelated to any bullish view, or a desk unwinding a hedge. Aggressor data is also purely transactional. It carries no information about size still resting passively in the book that hasn't traded yet, which can dwarf whatever aggressive flow just printed. Treat aggressor volume as a measure of urgency and initiative, not conviction or informed positioning. A single large aggressor print is also easy to over-read; it takes a sustained lean over many trades, not one, to say much about who is actually in control.

Over a five-minute stretch, Ethereum sees 1,800 ETH trade as buy-side aggressor (market buys lifting the ask) against 600 ETH as sell-side aggressor (market sells hitting the bid), a three-to-one lean toward buyers actively pushing the trade rather than waiting. Price only moves from $3,495 to $3,502 in that window, a modest change given the imbalance, which can mean resting sell orders are absorbing the aggression without breaking, or that the buying is being met by an equally deliberate seller working a large passive order just above the market.