i googled it. He got injured in week 17 of the 2016-2017 season. After his extension.
https://sportsinjurypredictor.com/player/david-johnson/7262
he got the extension on Sept. 8, 2018.
He injured his knee last game of the season on New Year's Day Jan. 1st 2017. Looked REALLY gruesome at the time, and "when the injury initially occurred, Johnson laid on the ground and feared the worst-case scenario. But he will just require six to eight weeks of "rest and rehab."
https://www.espn.com/nfl/story/_/id...n-knee-injury-not-serious-no-surgery-required
Then he broke his wrist in the first game of the 2017 season (Sept. 2017) and was out for the year. So there was the MCL damage and then wrist injury within 9 months of each other. Contract extension came out a full year later Sept. 8, 2018.
That said, I remember watching that first game since the MCL damage against Detroit in 2017 and thinking he did not look ANYTHING like the guy who was a beast in 2015/2016. That he looked demonstrably slower, not hitting the whole as hard, lacked the wiggle that he had the previous two years. Pretty much got laughed off the board and called an idiot. But Ouchie and I talked about it that day and then both of us saw the exact same thing last last year.
What might have happened was he got that knee scare... when he thought his career was over... and just basically has the football equivalent of the yips since then because he's never looked the same as he did before that Rams game. Combine that with the fact that he came in as an older rookie at 23 and the fact that the majority of stud RBs start to decline around age 28 (which he's 3 months shy of) and his time just could be up.
shame... he was electrifying those first two years.