The tunnel
Two pitches, one tunnel.
Deception is shared early flight. From the same arm slot, two pitches look like one out of the hand and only separate once the hitter has committed. Pick any two filed pitches and watch the shape split: which way each pitch wants to finish, and which one sets up the other.
Handedness
Four-seam
rides, stays true
The late split
Same window out of the hand, then each breaks its own way.
Slider
holds flat, sweeps glove-side
The endpoints are each pitch's sourced shape direction, taken from the specimen records. The shared tunnel window and the paths leading to each endpoint are a schematic of the shared-release idea, not a measured trajectory. A hitter's real reaction window depends on the arm, the release, and the pitch sequence. For the full picture of why tunneling works, see Sequencing & Tunneling.
The measured tunnel — release points, separation in inches, the tracked record — lives with the record-keepers: Baseball Savant ↗ and the FanGraphs model primer ↗. How to read them is its own wing: Reading Models.