5 things to watch: Lions at 49ers

2. SPEED, SPEED AND MORE SPEED

Two things jump out right away watching the 49ers' defense. One, their ability to fire off the ball upfront, and two, their overall team speed, especially at the linebacker position.

Fred Warner and Dre Greenlaw might be the best linebacker duo in the NFL. Their ability to play sideline to sideline in the run game and cover is as good as it gets.

"You could argue these two are right up there with Baltimore's two stacked linebackers (Patrick Queen & Roquan Smith). They're the best in football, in my opinion," Johnson said this week. "Normally, what we try to do on offense is we try to throw some eye candy out there and try to get them off kilter, but I think these guys have played so much football, together, within this scheme, that you can see they diagnose and read their keys very, very well. They're very instinctive football players."

The 49ers are a fast, attacking-style defense upfront and a group in the backend Johnson referred to as 'feisty.' Detroit's offense needs to start fast and combat the 49ers aggressiveness on defense with play speed and execution.