The old NFL adage is that defense wins championships, and the same can be said of fantasy football.
While defense and special teams (D/ST) units are often the last thing fantasy football owners are thinking about on draft night, they can have a big impact on team scoring from week to week.
That's why many fantasy football managers choose to stream defenses. It's better to target good-looking defenses in favorable matchups that to roll out the same defense every week even against top-tier offenses. Sure, some D/STs are matchup-proof, but those are few and far between.