The Battery
The pitcher and the catcher form the battery — the two players involved in every single pitch. The pitcher throws; the catcher receives, calls the pitch type and location, and defends home plate. A great defensive catcher also frames borderline pitches and controls the running game.
The Infield
First base, second base, shortstop, and third base ring the diamond. The shortstop and second baseman turn double plays and cover the most ground; third base is the ‘hot corner’ for hard-hit balls; first base anchors the most frequent force-out in the game. Infield defense quietly decides dozens of runs across a season.
The Outfield
Left, center, and right field patrol the grass behind the infield. The center fielder is usually the fastest and covers the most territory. Outfield arm strength matters most in right field, where the throw to third base is longest.
Why Position Matters to Prediction
Lineups are not equal. A team missing its starting shortstop or center fielder loses real defensive value, and the Ra model adjusts its expectations when a confirmed lineup is weaker or stronger than usual.