Not sure what you meant by proximate cause. What I was suggesting is that perhaps their workout regimen doesn't focus enough on maintaining flexibility.
And I am saying since they did not get hurt in OTAs, minicamps, training camp or preseason games (that we know of, they could have tweaked it almost any time), I would bet the cause was game action.
Bud Adams told me the franchise he admired the most was the Kansas City Chiefs. Then he asked for more hookers and blow.