What's With The Defense Lately?

I've noticed that they just let receivers off the line to make uncontested catches. It seems like they want to make the offense run more plays in the hopes that they will become impatient and make a mistake.


I still can't forget the last drive or two against SF when they seemed to be content with the 49ers running out of time. They did something similar against the Seahawks.

I'm guessing that there is some kind of thinking behind it, but I don't know what it is.