Strength of schedule is calculated from the opponents projected fantasy points allowed for the DEF position. The best rating is +16 which gives the player the advantage against the defense and indicates an easy opponent, the worst rating is -16 which gives the defense the advantage and indicates a tough opponent.
On paper this team should have fewer problems than it does, but for some reason the DL doesn't perform as you'd expect, whereas the secondary performs as exactly as you'd expect. Both are grave problems. Only one team gave up more plays of 40+ yds than the Lions (New Orleans), but whilst an addition of talent means we could be underselling the final sack tally, the poor secondary play won't be.