In order for GB or Chi to win the division:
2. The Lions must lose twice
As recently as two weeks ago, conventional wisdom held that the Lions had the easiest schedule remaining, but a lot has changed since then. Some of the former patsies of the NFC East have rebounded and, perhaps most importantly, the next 3 Detroit opponents are just terrible matchups for the Detroit defense for reasons we will get into momentarily.
at Philadelphia
Detroit has a spectacular run defense. By DVOA they rank 2nd overall in this category, and I don't think too many would argue with that ranking. Why then do I think the Eagles with Chip Kelly's typically run-based offense are a brutally difficult matchup for the Lions? The Eagles under Nick Foles excel in the two areas where Lions are weakest. Anyone who watched Tiquan Underwood torch them for 108 yards and 2 TDs a few weeks ago will be familiar.
According to Football Outsiders, the Lions are 27th against the pass. They are 28th against #1 receivers and that's a generous number as it includes the Matt Flynn debacle. They are, for my money, the worst secondary in the league. Moreover, while they excel in stopping the run, they are only 20th in the league defending against running backs catching passes. Here are some notable receiving stat lines against the Lions:
Alshon Jeffery - 5/107/1 TD, Brandon Marshall - 7/79/0, Martellus Bennett - 8/90/0
James Jones - 4/127/1 Jordy Nelson - 5/82
Josh Gordon - 7/126/0, Chris Ogbonnaya - 7/61/1
A.J. Green - 6/155/1
Dez Bryant - 3/72/2, Terrence Williams - 2/64/1
Brandon Marshall - 7/139/2, Alshon Jeffery - 9/114
Antonio Brown - 7/147/2
Tiquan Underwood - 3/108/2
The Eagles boast one of the game's best deep threats in DeSean Jackson and one of the best receiving RBs in LeSean McCoy. Moreover, since Nick Foles took over they've basically torched even good defenses. Scoring 24 points against Arizona is no small feat. The Eagles' defense isn't any good themselves, but they actually hold their own against #1 receivers (16th) and #2 receivers (10th). They struggle mightily against "other receivers" (29th) but we're talking Kris Durham here. Again, I'm not saying the Eagles will destroy the Lions, but this will be a very tough game for Detroit. Philly has won four straight games and looks like a different team lately (yes, part of this is an easy schedule). They are in a dogfight in the East, though, and will be highly motivated to win.
Home vs. Baltimore
Remember how I said the Lions have an elite run defense? The Ravens don't care because the Ravens can't run against anyone. Everyone the Ravens play (except the Bears) turns into the Lions. The Ravens don't do a lot well on offense, but one thing they happen to do well is throw the deep ball. Torrey Smith is still an elite deep receiver. Jacoby Jones isn't much, but he's a good deep receiver. These guys should be able to torch the Detroit secondary.
Baltimore may be bad on offense, but they're still a top-10 defensive unit (8th per Football Outsiders). They won't shut down Megatron (who does?) but should be able to keep their offense in the game. The Lions to watch in this game will be Reggie Bush and Joique Bell, as the Ravens rank 26th against backs out of the backfield.
Home vs. New York Giants
The Giants went from a laughingstock at 0-6 to a legitimate playoff contender by winning 5 of their last 6 games. Their defense, and Jason Pierre-Paul in particular, has gotten healthy lately and their season stats do not accurately reflect just how dangerous they currently are. Over the course of their last six games they have allowed 7, 7, 20, 13, 24, and 17 points. Football Outsiders agrees putting them 9th for the season and 6th using their weighted metric, which weighs more recent games more heavily. Better still; the Giants are 5th against #1 receivers (and 1st against #2 receivers).
On offense, the Giants again hit the Lions where it hurts. Victor Cruz is likely to torch this secondary. Rueben Randle is likely to chip in. Even the beleaguered Hakeem Nicks has shown some signs of life lately. With a healthy Andre Brown, who is no slouch in the passing game, the Giants offense is now formidable enough to capitalize on the Detroit defense.
At Minnesota
This is the lone good matchup for the Lions. They easily handled the Vikings back in week one and I expect they will again.
I don't expect the Lions to lose all three of those games, but no one should be shocked if they lose two. Keep in mind that some of the intangibles (awful penalties, terrible coaching) and things look rosier still.