also: slide · half slide · full slide · zone protection
Pass protection where linemen block a gap rather than a man, stepping together in one direction. Half slide does it on one side only, which is the version most teams actually run.
2 meanings, all below. Jump to the one you heard.
The entire offensive line steps in one direction and each lineman is responsible for the gap next to him rather than for a particular defender. Whoever comes through that gap is his. It does not matter who it turns out to be.
That is the point. A slide does not have to identify the rush before the snap, so a blitz from an unexpected place is picked up by whoever owns the gap it came through. The tradeoff is that the far end of the slide is exposed: sliding everybody one way leaves the backside edge to a single blocker, usually a back, against whatever shows up there.
full slide, zone protectionbig on big, half slideHalf the line slides, protecting gaps in one direction, and the other half blocks man on the defenders in front of them. Almost every offense that says it runs slide protection is running this.
The reason it is the default is that it splits the two failure modes rather than accepting either. The slide side handles pressure it did not identify, and the man side keeps a specific defender accounted for, usually the best rusher. Which side slides is normally decided by where the back is and where the pressure is expected from, which makes it a pre-snap decision rather than a fixed call.
half slidefull slide, big on bigSlide is the pass-protection cousin of zone run blocking and the same word does the same work: block an area, not a man. A coach who understands inside zone already understands most of a slide.
Usually installed second, after big on big, because it needs linemen who can identify a gap under pressure rather than a man they were shown pre-snap.