also: heads up · zero technique · two technique · four technique · six technique
Directly across from a blocker, on neither shoulder. The even numbers, and the alignment that deliberately refuses to declare a gap.
Nose to nose with the man in front of you. On the technique scale these are the even numbers: 0 head up on the center, 2 on the guard, 4 on the tackle, 6 on the tight end. The trade is the opposite of a shade. A shaded defender has already chosen a gap and can attack it; a head-up defender has chosen nothing, which means he can go either way and has to read the block before he does. That costs a step and buys the ability to play two gaps.
heads up, nose to noseshade, two-gappingHead-up alignments ask a defender to read and then react, which is a bigger ask of a young player than being told to attack one gap. That is a large part of why lower levels lean on shades even when the front is nominally even.