Intermediate

ツーシームファストボール/シンカー

Also known as: ツーシーマー, シンカー, 2シーム

Definition

ツーシームファストボールは2本の縫い目に沿って握る球種で、腕側(利き腕側)かつ下方向へ変化することが多く、三振よりもゴロを打たせる狙いで使われる。

細い縫い目に沿って握ることでバックスピンが減り、トップスピンの影響を受けた変化が生まれる。その結果、フォーシームより1〜4マイルほど遅くなり、投げる腕の側に曲がりながら沈んでいく。ゴロを打たせるタイプの投手は、ゾーンの低めで弱い打球を打たせて簡単なアウトを量産できるシンカーを重宝する。変化の質は腕の角度によって大きく変わり、腕の角度が高いほど横の変化が大きくなり、低いほど沈みが大きくなる。

Beginner tip

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.

Advanced note

Fine-tune the run-to-sink ratio by adjusting index-finger pressure. This means more index pressure increases arm-side run, more equal pressure with a downward wrist drive produces a truer sinking action.

Example

彼はツーシームを軸に投球を組み立て、右打者に対してゾーンの低めを攻めることでゴロ率58%を記録した。

Why it matters

分析においてツーシームとフォーシームを区別することは非常に重要だ。SwingVantageは、リリースポイントが崩れて本来異なる2つの球種が混ざっていないかを検知できる。

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. A release point that drifts lower than the four-seam reference. This means 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

SwingVantage compares release point coordinates and wrist angle between four-seam and two-seam reps to verify that the two pitches share the same early flight path. A diverging release point or visible arm-action change between pitch types shows up immediately in the side-by-side rep overlay.