NFL Fantasy Football Defense Rankings Week 15: Sleepers And Top Picks, Who To Start, Sit

The NFL essentially commanded defensive players to avoid violent collisions to the head in recent years, and now nasty knee injuries have littered locker rooms, especially this season. In Week 14, Arizona Cardinals rookie safety Tyrann Mathieu ripped his ACL and LCL, upping the number of season-ending knee injuries to at least 41 this year, a 64 percent jump since 2011, according to Bloomberg.