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 going to be Minnesota and Cincinnati who are facing two of the three teams with the lowest implied totals in Vegas this weekend. Cincy is going to be popular due to the matchup with the Browns who have allowed the most fantasy points per game to opposing defenses this season. It's certainly understandable why Cincy is a chalky pick, but Minny is the better option here. The Vikes are just a better defense as they rank sixth in Football Outsiders' Defense Efficiency Ratings (DVOA) while the Bengals rank 20th. And the Vikes also have a great matchup, even if it's not the best possible matchup. Minny will take on Jacksonville who allows the fourth most fantasy points per game to opposing defenses and actualy has a lower implied total in Vegas this week than Cleveland.
On top of all that, the Vikings are cheaper than the Bengals on FanDuel and FantasyAces, and the Vikings aren't that much more expensive on DraftKings. Perhaps Cincy will work on DK in cash, but Minny is the better option elsewhere. Both defenses will be popular and thus not great options in GPPs.
Sneaky Options
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.
Three defenses fall into this category this week: Seattle, Arizona and Denver. All three defenses rank top five in DVOA, and none figure to be too highly owned this weekend. All three teams are facing teams with below average implied totals, though none of their opponents have super low implied totals, which is why none of the defenses should be highly owned. Denver probably has the best matchup of this trio against Tennessee, but the Broncos are the most expensive defense of these three across the board. Generally the cheaper the better at defense, especially when you're picking a GPP option.
If pricing is the deciding factor here, Seattle is oddly cheap on DK at only $3,000. They're also the only favorite of this bunch, which is a plus for defenses as discussed above. Weather is also a factor this weekend, and the Cards are likely the biggest beneficiary in that regard with rain and high winds expected in Miami. The Cards are the same price as the Hawks on FD and $100 cheaper on Aces.
Bargain Option
Normally multiple options are discussed in this section as we search for the cheapest possible options on each site, but this week the same team is the cheapest possible option on all sites: Jacksonville. The Jags are an entirely decent defense as they rank 10th in DVOA, and they have a good matchup with Minnesota. The Vikes have the sixth lowest implied total of the weekend, and they have allowed the 11th most fantasy points to opposing defenses this season. In the last seven weeks, the Vikes have allowed at least five fantasy points to opposing defenses in each game. At just a couple hundred bucks over the minimum on DK and FD and at the minimum price on Aces, the Jags make for an excellent salary relief option.