also: tunnel · middle screen to a receiver
A screen where an outside receiver comes back inside to catch it and runs up a lane of blockers. The opposite direction to a bubble. It attacks a different mistake.
An outside receiver comes back toward the formation to catch a quick throw, while blockers, usually inside receivers and often linemen, get in front of him to form a lane he runs up. The name describes what the blocking makes.
The target is a defense whose outside defenders are getting depth or width at the snap. A corner bailing to protect deep and a linebacker widening to a bubble threat have both moved away from the space the tunnel runs through, and the play collects the ground they vacated.
It is the counterpart to the bubble rather than a variant of it: bubble goes out and attacks a defense that has not covered down, tunnel comes in and attacks a defense that has over-committed to width or depth.
tunnelbubble screen, screenTunnel and bubble are frequently installed together and read against each other, which is why they are worth learning as a pair even though each is a named play in its own right.
Harder than a bubble at youth level, because the receiver is catching the ball while moving toward pursuit rather than away from it, and because the blocking has to arrive in a specific place rather than just anywhere in front.