Inside the Legends Deck Sim Engine

Every outcome in Legends Deck — every swing, every stolen base, every diving catch — is the end product of a pipeline that starts with real MLB Statcast data and ends with a probability roll, and this guide shows you exactly how that pipeline works so you can build lineups that exploit it.

The Core Mechanics: From Statcast to Scoreboard

Legends Deck is free to play in your browser, but the engine underneath it is not simple. Here is the rating-to-outcome pipeline, step by step:

1. Real data becomes card attributes. Every card maps to a real MLB player, and that player's Statcast profile — exit velocity, barrel rate, sprint speed, OAA, and more — is distilled into card attributes: contact, power, velocity, spin, and fielding. A player who barrels the ball 15% of the time in real life carries a power rating that reflects it. The card is a compressed scouting report, not a fantasy invention.

2. Attributes become a normalizedRating. Each card's attributes roll up into a normalizedRating — a single number that lets the engine compare a rookie common card against a Hall of Fame legend on the same scale. This normalization is what keeps the sim fair: outcomes are computed from ratings on a shared scale, not from raw stats that would make modern players unbeatable.

3. Rarity and legendTier modify the ceiling, not the rules. Rarity tiers and the Hall of Fame legendTier system sit on top of the ratings. Higher tiers mean stronger cards, but every card — common or legend — plays by the same outcome math. A legend card wins because its ratings are higher, not because the engine gives it special treatment.

4. The sim resolves matchups probabilistically. When your lineup faces an opponent, the engine compares the relevant ratings — your hitter's contact and power against the pitcher's velocity and spin, your fielder's rating against the batted-ball quality — and rolls outcomes weighted by those comparisons. Better ratings shift the odds; they never guarantee the result.

That last point is the fairness guarantee. Because outcomes are probability-weighted rather than deterministic, a well-built budget lineup can beat a stacked one on any given day — but over a full season, ratings win. The engine rewards both smart construction and long-term thinking.

Step-by-Step Strategy: Building for the Pipeline

1. Read cards as Statcast summaries, not as names. Before you value any card, look at the attributes behind it. A famous player with mediocre underlying ratings will underperform a lesser-known player whose exit velocity and barrel rate drive a strong power attribute. The engine reads ratings, not reputations — so should you.

2. Balance your lineup across the attribute spectrum. The sim resolves both sides of the ball. A lineup stacked with power but weak in contact will produce volatile, streaky results. Pair high-power bats with high-contact hitters so your offense produces in every probability band, not just the home-run tail.

3. Never neglect fielding and speed. Fielding ratings convert opponent batted balls into outs, and sprint-speed-driven cards turn singles into doubles and steal bases. Most players over-invest in hitting because it's visible. The sim counts defense every single play — a cheap, high-fielding card often swings more runs than an expensive fourth slugger.

4. Use the marketplace to buy ratings, not tiers. In live trading and auctions, rarity commands a premium. But the sim only cares about normalizedRating and attributes. Hunt for lower-rarity cards whose Statcast profile outperforms their tier — they trade at a discount and sim at full value.

5. Draft for fit in auctions and drafts. When building through drafts, fill your weakest attribute category first. The engine punishes holes more than it rewards surplus. Replacing your worst fielder adds more expected wins than adding a third power bat.

6. Track results over volume, not single games. Because outcomes are probabilistic, judge a roster move after a meaningful sample. One bad series is variance; twenty bad games is a ratings problem.

Common Mistakes

• Chasing rarity over ratings. A high-tier card with mediocre attributes loses sims to a common card with elite underlying data. The tier system affects ceiling, not outcome math.
• Ignoring fielding entirely. Every batted ball your opponent puts in play tests your defense. Weak fielding is a leak that runs all game.
• Overreacting to small samples. The engine is probabilistic by design. Benching a strong card after three bad games is punishing variance, not fixing a problem.
• Paying auction premiums for famous names. The marketplace prices reputation; the sim prices ratings. Buy the discount.
• Building a one-dimensional offense. All power, no contact produces boom-or-bust results that lose close games you should win.

Advanced Angle: Exploit the Matchup Layer

The engine resolves pitcher-versus-hitter matchups using opposing attributes — velocity and spin against contact and power. Experienced players build lineups with *attribute diversity* specifically to avoid hard counters. If your entire lineup is built the same way (say, all low-contact power hitters), a single high-velocity, high-spin pitcher suppresses your whole offense at once. Mix profiles so no single opposing ace can neutralize your lineup in one matchup. Diversity isn't just balance — it's counter-proofing.

Related Reading

• What Is Barrel Rate? — the Statcast metric behind the power attribute.
• Exit Velocity, Explained — how raw batted-ball speed feeds card ratings.
• OAA and the Fielding Attribute — why defense wins sims.
• Legends Deck Marketplace Guide — buy ratings, sell reputation.
• Rarity Tiers and legendTier — what the Hall of Fame tier actually changes.