Guys play with injuries all the time. They evaluate risk versus reward. Guys play with partially torn ACLs, broken bones, sprained everything. Nothing could be more common than for at the end of the season to hear about some players getting surgery for injuries they played through that often the public wasn't even aware. Then there are guys like Mayfield who is playing while having his shoulder held in place with a brace. He'll have surgery when the season is over. Might it get worse? Yes. But that's a calculated risk the team and player have agreed to take.
It just turns out that SJDs injury was more than he can play through, even though he was given treatment and rest and it seemed to be responding.
But to start pointing fingers of blame at team trainers is simply not warranted or fair. The Rams under McVay have always been conservative regarding injuries. It also known that players, themselves, will often downplay the severity of an injury to the team because they don't want to be sat down.
