also: GDB · GOD · gap on down · blocking rules
Two blocking rules with near-identical acronyms that resolve differently. The difference is whether you block the man standing on you.
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The playside rule for gap-scheme runs like power, counter and buck. In order: block anybody in your inside gap; if it is empty, block the man over or inside the lineman next to you; if that is empty too, climb to the linebacker those rules would have taken you to. Note what is missing: a defender lined up head up on you is not in the list at all. The rule is a strict inside-out priority, and a man head up is never the most dangerous defender to a play going inside of him. Who ends up accounting for him varies by play and it is not always a puller.
GDB, gap down backerGOD, zone-scheme rulesThe most common youth blocking rule. In order: block anybody in your gap; if it is empty, block the man on you; if that is empty, block down inside. It never sends anybody to a linebacker, and its second step is the one gap-down-backer deliberately skips, which is the whole difference between them. It suits a scheme with no pullers, where every lineman has to account for the man in front of him because nobody else will.
GOD, gap on downgap-down-backerGOD is close to universal in youth football because it is teachable in one practice and needs no pulling. GDB arrives with a gap scheme, and the switch is a real install cost, because a lineman who has been taught to block the man on him has to be untaught.