Intermediate

투심 패스트볼 / 싱커

Also known as: 투심, 싱커, 2심

Definition

투심 패스트볼은 두 개의 솔기를 따라 쥐고 던지며, 대체로 투수 쪽 팔 방향으로 그리고 아래로 움직여 삼진보다 땅볼을 유도한다.

좁은 솔기를 따라 쥐면 백스핀이 줄고 톱스핀 영향을 받는 무브먼트가 가능해진다. 그 결과 투수의 포심보다 대체로 1~4마일(약 1.6~6.4km/h) 느리고, 던지는 팔 쪽으로 휘면서 가라앉는 pitch가 만들어진다. 땅볼 유도형 투수는 존 아래쪽에서의 약한 컨택트가 손쉬운 아웃을 만들어내기 때문에 싱커를 소중히 여긴다. 무브먼트 프로파일은 팔 각도에 따라 크게 달라진다. 팔 각도가 높을수록 수평 무브먼트가 커지고, 낮을수록 가라앉는 정도가 커진다.

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

그는 투심을 주무기로 우타자 상대로 존 아래쪽을 공략하며 땅볼 유도율 58%를 기록했다.

Why it matters

분석에서 투심과 포심을 구분하는 것은 매우 중요하다. SwingVantage는 릴리스 포인트가 무너져 서로 달라야 할 두 pitch가 뒤섞이고 있는지 표시해 줄 수 있다.

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.