also: wham · wham trap
A back or tight end crossing the formation to trap a defensive lineman who has been deliberately left unblocked. A trap block by somebody who is not a lineman.
The offensive line deliberately leaves an interior defender unblocked and lets him come, and a back or tight end crosses the formation and blocks him from the side as he does. The defender's own aggression is what puts him where the block can reach him.
Structurally it is a trap executed by a back or tight end instead of a lineman. No lineman has to leave, so the interior stays intact and the front cannot spot the block from a puller's movement.
whamkick out and log, sift