It's a combination of personnel and coaching and scheme. And that's why when it looks bad, it looks really bad IMHO...
There were so many plays to point to today on Defense if you want to get frustrated... But I'll tell you the one that drove me the most crazy, and it's plays like this that always drive me insane with this team. The Bills have the Pats pinned at their own one and it's 2nd and 10... The Pats line up in Shotgun so they are going to let the kid pass out of the endzone... If you don't want to call a pressure on that play... OK... But what the Bills do...what they ALWAYS seem to do to drive me insane. The CB drops to beyond the 1st down marker and they give up a free and easy 7-8 yards making the 3rd down much easier... A play later it's 1st and 10... And that happens over and over and over again with this Defense... Free yards... And teams know where they can get them and how to get them off this Defense and the scheme. How many 3rd and 7-10's do we see an open receiver 5-8 yards down the field who turns and gets a couple yards easily to keep the chains moving? I get McD's Defense is predicated upon keeping the play in front of you but teams are well onto that now and it's just too easy...
And don't get me started on anything misdirection... Oh my...