Strength of schedule is calculated from the opponents projected fantasy points allowed for the DB 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.
Grimes was a top-15 fantasy defensive back in 2010 with the Atlanta Falcons, topping 85 tackles and intercepting five passes. However, in the two years since Grimes has only 55 tackles total, and the seventh-year pro missed nearly the entire 2012 campaign with a torn Achilles tendon. Grimes' rehab has reportedly progressed well though, so he might be worth a late look on draft day if your IDP league requires cornerbacks.