It's very nuanced, that's for sure. There's judgment of individual play, and how do they perform as a unit. It's about knowing your assignments, and your teammates'
and being able to make adjustments pre-snap and on the fly post-snap, reacting to stunts and crosses. You need to watch the individual on each and every play to know if he's looking lost, or being dominated by opponents. Does he commit allot of penalties. Holding is a sign of laziness, desperation and bad technique, false starts are all mental, focus and concentration. Some fans have unrealistic expectations regarding offensive lines. With the level of athleticism on D-lines these days, nobody can block anyone forever. 3 seconds in pass pro is a long time. Keep your opponent off your QB for 3 seconds and your good. Run game is more obvious. Do you open holes, or are you stoned? Like so many others have said, as fans you know it when you see it, stats cant really tell the story.