Why large orders move price
Every market order you send consumes resting liquidity at the best available price. If the bid size is 50 contracts and you market-sell 100, you consume all 50 at the current bid and then the remaining 50 execute at the next lower price level. Price moved not because of fundamental information, but purely because your order ran out of available liquidity.
This is price impact — the market moves against you as a direct result of your own order. For small retail orders in liquid futures, the impact is minimal (a tick or two). For institutional orders of thousands of contracts, the impact can be significant enough to move the market by a full point or more.
Price impact is nonlinear. A 100-contract order doesn't have twice the impact of a 50-contract order — it may have 3-4 times the impact if the order book is thin above a certain size. The shape of the order book (how much liquidity exists at each price level) determines the impact function.
The depth of market (DOM) shows you the available liquidity at each price level. Deep books (many contracts available at each level) absorb large orders with minimal price impact. Thin books (few contracts at each level) are moved easily by small orders. Trading in thin conditions amplifies execution cost.
Measuring and minimizing slippage
Slippage = (actual fill price - expected fill price). For a market buy, slippage is typically positive (you paid more than the last traded price). For a market sell, slippage is negative (you received less). Slippage represents a direct cost that is often underestimated by retail traders using historical data without simulating fill quality.
To minimize slippage: use limit orders instead of market orders when speed isn't critical. Break large orders into smaller pieces across time (TWAP) or across liquidity (participate at a fixed percentage of volume). Trade during high-liquidity periods (first 90 minutes and last 60 minutes of the regular session for US futures). Avoid trading immediately after major news when spreads widen.
One counterintuitive insight: in fast markets (immediately after CPI or NFP releases), liquidity is temporarily poor because market makers widen spreads aggressively and pull quotes pending repricing. The very moment when momentum traders want to enter is often the worst time for execution quality.
Information leakage
When a large institution needs to trade a significant quantity over time, its gradual accumulation can be detected by sophisticated participants — particularly HFT firms — who then "front-run" the flow. The institution's buying pushes prices up before it finishes, making its average cost worse.
To minimize information leakage, institutions use sophisticated order routing, dark pools, and algorithmic strategies designed to appear random while efficiently executing. Randomizing trade sizes, timing, and venues makes the pattern harder to detect.
For retail traders, information leakage in the standard sense isn't relevant. But the concept applies to being obvious about your level entries — if you consistently place limit orders at obvious round numbers (which many other traders also target), you compete for fills with many others and may face adverse selection when those levels do trade.