“4 Lock” is a defensive coverage concept that typically stems from a Cover 4 defense (quarters) structure, where the secondary plays four-deep, but with “lock” principles applied to specific receivers.

In 4 Lock, one or more defensive backs—usually corners—“lock” onto their assigned receiver in man coverage, rather than playing their traditional zone responsibility. Meanwhile, the safeties and remaining defenders maintain a quarters or match-based structure over the top. This allows the defense to eliminate key threats (like top receivers or vertical routes) while still keeping the integrity of a split-safety shell.

In short, 4 Lock blends man coverage on priority targets with zone/quarters support behind it, giving the defense flexibility to match up without sacrificing deep coverage structure.