Like many here probably have, I have read up quite a bit about ACL injuries. Being not the least bit medically knowledgable, I can only go by what I read.
And generally what I read says: 1) Some of the ACL tears are a mystery. They just happen. Or better there's no real explanation as to how a guy could take shot after shot and not have a tear, but then he's standing there "combing his hair" (read: non-contact).....and boom! There it goes.
2) The belief today, more and more, is that the ACL that tears is often already traumatized in some way and therefore its strength has been compromised. Sure, a single hit can be so severe that it can tear an otherwise healthy ACL. But where there isn't a particularly violent hit, and when there doesn't seem to be any extenuating circumstances, the current wisdom is that the ACL already wasn't healthy.
We read all the time about coaches saying (regarding his Q
that those hits add up. So keeping the QB clean is really important, especially if he's not a running kind and thus doesn't possess that body type. Doesn't have the genetic make-up that gives him stronger ligaments, muscles, etc. Maybe we can't exactly explain HOW those hits add up, but the anecdotal evidence is that they do. QBs that get sacked and hit a lot, or run a lot, get hurt.....a lot.
Bottom line: From a medical viewpoint the Wentz injury was almost predictable. Just as the DeShaun Watson injury was almost predictable. When? How? Not predictable. Coaches and teams don't want to think about this reality because sometimes these guys are so incredible at what they do. And if you take the run element away from them, it can negatively affect their entire game. These guys didn't start running and taking hits when they got drafted. It was their style probably in High School, which is what got them noticed to get a scholarship for college. And, with the trend of running QBs in college, they fit. But: those hits add up. And if they take that with them to the next level, especially so in the NFL, then the odds of injury increase.
I have no idea if these medical opinions (theories?) are correct. But, man, after watching the NFL for 50 years, it is not only logical, it is darned hard to argue against. Having a running QB as your Franchise QB carries a higher risk than the prototypical drop back passer for injury. Of course, drop back passers who don't run get ACL's, too. But by not running, a substantial injury risk is removed.