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.
Consider the blitz-happy New Orleans defense a solid play against a mistake-prone St. Louis offense. During the last month, the Saints averaged 3.5 sacks and 0.5 forced turnovers per contest. In the same time frame, the Rams offense, in three games played, allowed an average of three sacks per game and turned the ball over an average of one time per outing.
Another team transitioning their base defense. Sadly, they are less well equipped to deal with it than some others. This is going to be a long year defensively for the Saints, having struggled to break the 35 sack barrier for the past 3 seasons. In 2011 their sack leader was even a safety. It's even harder now to envisage where those pressures are going to come from on a team that surrendered a league high number of big passing plays.