Sure, some free agents can affect the D/ST rankings, but in general the stoutest of defenses and most dynamic of special teams are already in place. It means the initial rankings and tiers are unlikely to change.
What can dramatically affect the value of D/STs in your leagues are scoring systems. Pay special attention to whether your league adds (or subtracts) significant points for yards or points against.
In general, though, the fundamentals are the same: Elite units have what every big-time championship-caliber defense is predicated on: Stopping the run. If you can accomplish that, you can then tee off on quarterbacks and make Sundays awfully long for opposing offenses.
Sleeper: Detroit Lions
If you sort your three-year averages of D/STs in your fantasy football league, the team dead last is very likely the Lions. But they have bolstered their unit up front with the burgeoning dominance of sophomore DT Ndamukong Suh and the drafting of line-mate Nick Fairley from Auburn. That is going to help them take away the running game -- albeit in an NFC North division that is home to Adrian Peterson, Matt Forte and Ryan Grant. The Lions are going to surprise people, though, making them a solid backup D/ST on draft day.
Breakout: New York Giants
Yes, the Eagles and Cowboys have explosive offenses in their division, but the Giants have the potential to be an explosive defense. Coordinator Perry Fewell has fueled an attacking unit that focuses on generating turnovers. The Giants led the NFL with 23 forced fumbles -- no one else had more than 18 -- and their cross-over games this season are against the weaker-QB divisions of the AFC East (save for Tom Brady) and the NFC West. That should lead to more interceptions and defensive scores from a secondary that added a premium cover corner in the draft and is famously strong and deep along the line.
Also, Eli Manning figures to cut down on his league-high 25 INTs, improving field position and making the unit more stingy in points against. The Giants are going to be selected well into the second tier of D/STs, but they are talented enough to outscore everyone with sacks and turnovers.
Bust: Arizona Cardinals
Standard leagues were led by the New England Patriots and Cardinals last year because those D/STs scored the most defensive touchdowns (Pats had nine and the Cards 10). It boils down the quality of quarterbacks you play, and the Cards played their division games against suspect quarterbacks. The Rams have Sam Bradford ready to take off in Year 2, but the Seahawks and 49ers">49ers have to try to get back with subpar passers. Other than the favorable schedule the Cardinals will face, this really isn't a talented-enough unit to consider drafting in fantasy.
Like was said above, stopping the run makes you a championship-caliber defense. These teams do it better than anyone. We list the Packers third, because they are more of a wide-open offensive team that could give up the garbage-time scores the Jets or Steelers won't.
This group represents the last of the D/STs that warrant starting on an every-week basis. The best strategy with picking your defenses is getting a couple of solid ones after the middle rounds and playing the matchups. You won't need to sit these units very often -- unless they are facing an elite-tier QB.
It is debatable these are starting D/STs, but there is talent here. All four of these units are top-12 at stopping the run. A few breaks in the win column (save for the Falcons, who were the NFC's No. 1 seed a season ago) will make these teams a lot more valuable than their modest draft position.
The Saints are still an elite team that can overwhelm opponents, which allows them to take the running game out of play. It is tough to stick to the ground game when the fast-break offense is already up three scores. The Lions and Chiefs are young and talented with the potential to surprise us in fantasy.
You wouldn't want to trust these defenses on a regular basis, but when they are facing a suspect quarterback, they can come in handy. If you're picking a backup D/ST, your choices should end here. Not all 12 teams in standard leagues are advised to burn a roster spot in their draft on a second defense.
While these teams probably shouldn't be drafted, they will frequently be under consideration when your primary unit is facing an elite-tier QB. The only reason these teams are just off the draft radar is because the upside just isn't there. They are mediocre at best.
These teams are likely to be improved from a year ago, but they don't promise to do anything in any of the categories we really care about: Sacks, fumble recoveries, interceptions or kick returns.
You must be under a rock if you dare to draft these teams in after the years they suffered through last season. While stopping the run can make you a great defense, being a sieve in the secondary can really make you look terrible. The Texans, Broncos and Jags easily had three of the worst pass defenses a year ago. The Panthers, meanwhile, lost their defensive-minded head coach -- not that he was doing much with their defense.
Eric Mack writes fantasy for SI.com. You can mock him, rip him and (doubtful) praise him before asking him for fantasy advice on Twitter @EricMackFantasy. Hit him up. He honestly has nothing better to do with his free time.
ON SALE SOON: Sports Illustrated's Fantasy Football 2011 issue tells you where all the free agents landed and what their fantasy impact will be, along with the critical draft strategy and statistical analysis you need to win your league. Available in mid-August.