Pitch tunneling is the art of throwing different pitches on identical early trajectories so the hitter can't differentiate them by the decision point — then breaking them apart afterward. Concept popularized by Driveline and Baseball Prospectus.
Two key metrics: (1) Tunnel Point Distance — how similar the trajectories are at ~23 ft from home plate (where the batter commits). (2) Break Differential — how much they separate after that point.
The ideal: same path until commit, very different paths after. A high four-seamer and a low curve thrown from the same tunnel force batters to swing at one and miss the other entirely.
Koji Uehara's four-seam / splitter combo, Kodai Senga's ghost forkball, and Roki Sasaki's four-seam / slider pairing are classic examples. Tunneling sits alongside Stuff+ (pitch quality) and Location+ (command) as a third axis: sequencing.
→ Related: Stuff+ & Location+ / Spin Rate / Pitch classification