Imma be honest and say that I can't tell whether people are running a zone or man blocking scheme just by watching a game real time as a fan. There are hints, but nothing is a 100% reliable tell without knowing how it is coached. If I watched film of a play over and over - seeing how the defense is aligned, watching each lineman individually multiple times to see what he's doing as the play develops - I can usually figure it out. But I can't do that during a game, especially one I'm emotionally invested in. I can read blocking technique that way but not scheme.