Two-Seam Fastball / Sinker
Also known as: two-seamer, sinker, 2-seam
The two-seam fastball is gripped along two seams and usually moves arm-side and downward, inducing ground balls rather than strikeouts.
Gripping along the narrow seams reduces backspin and allows topspin-influenced movement. The result is a pitch that usually runs 1–4 mph slower than the pitcher's four-seamer and breaks toward the throwing arm side while sinking. Ground-ball pitchers prize the sinker because weak contact down in the zone produces easy outs. The movement profile varies significantly by arm slot — higher arm angles produce more horizontal run; lower slots produce more sink.
Start by simply shifting your four-seam grip to the narrow seams without changing anything else in your delivery and let the natural topspin create movement before trying to add extra arm-side run.
Fine-tune the run-to-sink ratio by adjusting index-finger pressure: more index pressure increases arm-side run, more equal pressure with a downward wrist drive produces a truer sinking action.
Example
He lived on his two-seamer, inducing ground balls at a 58% rate by working the bottom of the zone against right-handed hitters.
Why it matters
Your two-seamer and four-seamer should look the same out of the hand and only move differently afterwards. If your release drifts between them, the two pitches blend into one. Motion Lab does not tell pitch types apart, so compare clips of each filmed from the same spot.
How it shows up on video
On video, the two-seam fastball should look identical to the four-seamer through the first third of flight. Divergence in trajectory becomes visible only in the final 15 feet. Common errors on camera include a change in arm action that telegraphs the pitch before release, a noticeable wrist roll that produces sidespin rather than the intended run-and-sink movement, and a release point that drifts lower than the four-seam reference — blending the two pitches into one undifferentiated offering.
Common mistakes
- Visibly changing arm action or wrist position when switching from the four-seamer to the two-seamer, telegraphing the pitch to attentive hitters
- Releasing the ball with excess sidespin rather than the run-and-sink tumble, turning the pitch into a flat slider with no ground-ball value
- Locating the two-seamer up in the zone where its downward movement is neutralised and its slower velocity becomes easy to elevate
- Gripping the seams so tightly that arm speed drops, making the velocity gap between the four-seamer and two-seamer larger than intended and obvious to hitters
In SwingVantage Motion Lab
Motion Lab does not know which pitch you threw and does not track the ball. As a result, it cannot compare your two-seamer's release or flight with your four-seamer's. Film both from the same spot and compare the arm action side by side.
Related terms
- Four-Seam FastballThe four-seam fastball is the most common pitch in baseball — gripped across all four seams — and is usually the hardest, straightest pitch a pitcher throws.
- Arm AngleArm angle is the vertical orientation of the throwing arm at release — from over-the-top through three-quarter, sidearm, to submarine — and it shapes both the pitch plane and movement profile.
- Horizontal BreakHorizontal break is the lateral movement a pitch generates from spin, measured in inches to the arm side (positive) or glove side (negative).
- Induced Vertical Break (IVB)Induced vertical break is the vertical movement a pitch achieves purely from spin, measured against a hypothetical spinless ball — isolating the Magnus effect from gravity.
- Seam-Shifted Wake (SSW)Seam-shifted wake (SSW) is an airflow effect where off-center seams disturb the air unevenly. It causes movement that spin rate or axis alone can't predict.
Available in other languages
Related guides & benchmarks
Put this into your swing
SwingVantage can spot this in your own swing — free to start.
See a sample Baseball report first