It was a breakthrough game in which the Madden cover boy and best WR in the game ran wild, especially in the second half, despite the fact that he's still playing at a mere fraction of his full effectiveness.
Several times he came off the field wincing. He's not just playing with lowered effectiveness—he's playing through a lot of pain.
Still, Johnson's stat line was 207 yards and a touchdown in a losing effort. For reference, Christian Ponder had a total of 221 passing yards.
But despite Johnson's numbers, he didn't dominate the entire game. At halftime, Johnson had three catches for 25 yards.
So what changed?
In the first half, the Vikings gave Johnson zero cushion. You can see the corner playing about a yard off the line of scrimmage here:
He immediately puts his hands on Johnson, trying to bump him off his route. On this play, Stafford threw a checkdown swing pass to Joique Bell, who couldn't handle it.
That worked, because the initial corner caused enough disruption to affect a short timing route, and there's a safety waiting for Johnson to create separation with the corner down the field.
When the Vikings didn't try to bump Johnson, instead turning immediately to keep up with him down the field,
The Vikings started playing even further off the line in the second half, often allowing Johnson a free release. Since the Vikings had the lead, the idea was to play a softer zone to keep Johnson from getting deep, but the plan backfired.
Look at all the space Johnson is being given to maneuver here:
And look how it ends up for the defense:
The corner played him five yards off the line, trying to keep Johnson in front of him. Instead, he gave up 20 yards as Johnson was able to find a soft spot over the middle.
Of course, if stopping Johnson were as simple as playing tight double-man coverage, he wouldn't be the best receiver in football.
Because even when the corner tries to bump him, and there's extra coverage downfield,
this can still happen 51 yards later:
But why? Johnson is being played the same here as he was when locked down in the first half, so why did he get so far downfield on a play when he was being played tightly on the line?
Well, first off, Vikings safety Harrison Smith was late with the help, which raises one of the problems with covering Johnson: Even when he's double-covered, the coverage has to be perfect.
But a bigger part of it is that Johnson and the Lions adjusted to the close coverage. When the corner played off about four or five yards, Johnson took advantage. So if the corner is playing right on the line, how does Johnson adjust?
He plays off the line himself.
Sure, it means it takes him longer to get down the field, but it also gives him two or three steps to build up some momentum, which means it's much more difficult to slow him or change his course when the defender gets to him.
That's the benefit of being fast and tall and weighing 235 pounds with strength to match. Those physical attributes make Johnson a tough cover at all times, but there is a reason the Lions aren't sending Johnson 50 yards down the field and letting him lay out or go up for it on every play.
After last season, NFL defenses realized there was no point in trying to win a jump ball against Calvin Johnson. Johnson high-points the ball and out-leaps everyone to get it.
Instead, safeties are starting to focus on what happens after the catch. In other words, secondaries are trying to make sure he doesn't complete the process.
Here's Smith doing what he can to make Johnson drop his 50-yard reception:
And even though Johnson held onto the ball, this is the aftermath:
Johnson is tough, but he's human. He's already injured, and defenders are starting to understand that the best way to stop Johnson's jump-ball ability is to simply hit him as hard as possible when he comes down to separate ball from receiver forcefully.
The Lions are probably not keen on putting their $130 million man in harm's way just because deep jump balls are the only way they can move the ball. Johnson isn't just a big target for the quarterback—he's also a big target for opposing defenders.
That doesn't mean it's a bad idea to let Johnson go down the field and use his size and athleticism to dominate the defense. This is football. Everybody is going to get hit at some point, and injuries happen.
But for a player like Johnson, who is critical to the success of the Lions as a whole, why would you put him in position to get hurt any more than absolutely necessary?
Especially when he can put up 200 yards in a game after only doing it once?