Active Spin

Simple explanation

Not all the spin on a pitch turns into movement. Active spin is the share that does. At 100%, every bit of spin goes into bending the ball.

Backspin, topspin or sidespin all count as active as long as the ball spins at a right angle to its flight. The more a pitcher twists his wrist and releases the ball like a football, the more spin goes around the direction of travel and the lower the number.

Benchmarks

32%

Slider

47%

Cutter

73%

Curveball

91%

Four-seamer

Median for each pitch type among pitchers on the 2026 Savant active spin leaderboard (50+ pitches of that type).

Detailed explanation

Each pitch type has its own normal. On the 2026 Savant leaderboard, pitcher medians were 90.5% for four-seamers, 90.0% for changeups, 87.2% for sinkers, 73.3% for curveballs, 50.5% for sweepers, 47.0% for cutters and 31.7% for sliders. For sliders and cutters, a low number is part of what makes them what they are.

Sometimes the movement predicted from spin alone doesn't match the actual movement. The gap is put down to seam-shifted wake, the seams changing the airflow around the ball, and FanGraphs' Stuff+ feeds it into the model as axis differential.

Multiplying by spin rate gives a rough idea of how much spin is actually doing work. A 2,400 rpm four-seamer with 90% active spin has 2,160 rpm worth of spin making it move.