The key with defenses is finding defenses that will face a lot of passing plays. Fantasy point-scoring events like interceptions and sacks occur exclusively on passing plays, and fumbles actually occur more on passing plays than running plays. Defensive touchdowns are difficult to predict, but they're also more likely to occur on passing plays with 53 pick sixes last year compared to only 33 scoop 'n scores.
One of the best ways to identify defenses that will face a lot of passing plays is identifying Vegas favorites, preferably home favorites. And obviously the lower the opponent's implied point total, the better the matchup for the defense.
Premium Options
The chalk this week is most likely going to be Seattle and Kansas City. Both teams are facing offense with an implied total in Vegas under 19, and both defenses rank top eight in fantasy scoring so far this season. And there's nothing fluky about ther fantasy performance. According to Football Outsiders' defense efficiency ratings (DVOA), the Seahawks and Chiefs defenses rank third and ninth, repsectively.
Seattle may have the better defense all things being equal, but thanks to their respective opponents, all things are not equal. The Chiefs will have the better matchup as they host the Jags who have allowed the eighth most fantasy points per game to opposing defenses. Meanwhile, the Seahawks will host the Bills who have yet to allow an opposing defense to score double digit fantasy points against them. For that reason, Kansas City is likely to be the most popular play of the weekend. So if you're looking to be contrarian, fade the Chiefs.
Sneaky Option
This category is reserved for good defenses that may be overlooked in a given week for whatever reason, providing you with the opportunity to roster a really good unit with a lower ownership rate.
All the ownership on Kansas City and Seattle should draw enough ownership away from Minnesota for them to be a bit overlooked this weekend. The Vikes are still the highest scoring fantasy defense so far (though Denver has almost caught them), and Minny ranks fifth in DVOA. Their matchup with the Lions is below average, but it's not any worse of a matchup than the Bills are for Seattle. And Vegas really likes the Minny defense this week as the Lions have the lowest implied total of the weekend. It's not like the Vikings are going to barely be owned, but there should be at least three defenses with a higher rate of ownership. That makes the Vikes a GPP option. Hell, they're a cash option as well.
Bargain Options
The cheapest possible option on FanDuel is probably the Giants who rank 10th in DVOA. The Giants D/ST has been completely boom-or-bust this season with five of seven games in which they scored 1, 0 or -1 fantasy point(s). But in their other two games they've scored 15 and 20 fantasy points. This could be another week where they go big against an Eagles team that has been friendly to opposing defenses in recent weeks. In their last four games, Philly has allowed opposing defense to score at least seven fantasy points in each game. Vegas is also on board with the Giants as the Eagles have the fourth lowest implied total of the weekend.
The cheapest possible option on DraftKings is Green Bay. The Packers rank eighth in DVOA, and they'll host the Colts who have allowed the seventh most fantasy points per game to opposing defenses. Indy's offensive line ranks dead freakin' last in FO's pass protection stat, Adjusted Sack Rate, and Green Bay's D-line ranks fourth in the defensive version of Adjusted Sack Rate. That's a mismatch of the highest order that puts Green Bay's D/ST in an excellent spot to score fantasy points.