In fantasy football no position can be more unpredictable from season to season than team defenses, as personnel changes, injuries and scheme switches can all have a huge impact on a defensive unit from one year to the next.
However, every team has to have one, so as a service to you fantasy football fanatics preparing for drafts this weekend here's a look at my top 15 team defenses for the 2012 season.
Additionally the defense, led by linebackers Patrick Willis and Navorro Bowman, returns all 11 starters this season, and that's enough to garner the 49ers this season's top spot.
No team in the National Football League got to the quarterback more times in 2011 than the Philadelphia Eagles, who were led by defensive ends Trent Cole and Jason Babin.
Cole and Babin combined for 29 of the team's 50 sacks, and with an improved linebacker corps featuring middle linebacker DeMeco Ryans and rookie Mychal Kendricks, the Eagles should be terrorizing opposing signal-callers again in 2012.
The Pittsburgh Steelers were the NFL's stingiest defense last season in terms of yards allowed to opposing offenses, giving up just under 272 yards per game total, which was less than a pair of NFL teams allowed through the air alone.
Granted, you'd like to see Dick LeBeau's zone blitz generate more big plays, but those can be fluky, and if the Steelers do get an uptick in that area this year they will return to their rightful place among fantasy football's elite defensive units.
The Baltimore Ravens have fielded one of the NFL's most formidable defenses for several years now, but the team received some devastating news this year before training camp even got underway.
The loss of reigning NFL defensive player of the year Terrell Suggs to a season-ending Achilles injury is a crushing blow to the Ravens' pass rush, and it will be up to linebacker Ray Lewis, safety Ed Reed and the rest of Baltimore's defensive stars to pick up "T-Sizzle's" slack.
It may seem somewhat strange to see the Green Bay Packers defense listed this highly, especially given that the team fielded the most porous defensive squad in the National Football League in 2011.
However, the Packers are also a team that historically generates a lot of big plays, as the bizarre blitzes and coverage packages unique to Dom Capers' zone blitz have a tendency to force opposing quarterbacks into mistakes.
Green Bay ranked third in fantasy points among team defenses last year, and if the team can improve on a pass rush that was 27th in the NFL in sacks last season then there's no reason to think that the Packers won't once again post top-five fantasy numbers defensively.
The Houston Texans defense experienced a renaissance in 2011 in their first year running a 3-4 under defensive coordinator Wade Phillips, going from 30th in the NFL in total defense in 2010 to second a year ago.
Anchored by a number of young stars including linebacker Brian Cushing and defensive end J.J. Watt, and with 2011 NCAA sack king Whitney Mercilus softening the loss of Mario Williams, the Texans should once again be a fearsome defensive unit in the upcoming season.
The Chicago Bears were fantasy football's second-ranked team defense in 2011 in CBS Sports default scoring, propelled in part to that lofty ranking by an eye-popping nine total touchdowns on defense and special teams.
That sort of gaudy statistic may not be sustainable, but with a decent pass rush led by defensive end Julius Peppers and one of the NFL's most dangerous return men in Devin Hester, the Bears defense is a solid fantasy option for owners who wait a bit before selecting a starter at the position.
There may well be no more fearsome defensive front in the NFL than that of the New York Giants, as defensive ends Jason Pierre-Paul, Justin Tuck and Osi Umenyiora have all shown a propensity for getting after the quarterback.
Even with Tuck on the shelf for much of last season, the Giants still ranked third in the NFL with 48 sacks, which equates to the sort of fantasy production that makes the Giants a serviceable, if not spectacular, starting fantasy defense.
The Buffalo Bills were an anemic 24th in the NFL in total defense last year, and the team took major steps to address that deficiency in the offseason.
The Bills are making the switch to the 4-3 defense in 2012, and with newcomers Mario Williams and Mark Anderson joining defensive tackles Kyle Williams and Marcell Dareus, the Bills now possess one of the stronger front fours in the NFL, at least on paper.
The Detroit Lions were fantasy football's top defense last season, so you may be wondering why they only check in at 10th on this list.
Granted, the Lions' pass rush, led by defensive end Cliff Avril and tackle Ndamukong Suh, ranked a very respectable 10th in the league in sacks last year, but the biggest reason for Detroit's lofty ranking was their league-leading seven defensive touchdowns.
That sort of production simply isn't sustainable, but if you can get the Lions a bit later in fantasy drafts they can potentially be a very solid value play, especially given a tasty Week 1 matchup at home against the Rams.
Given their ranking of 31st in the National Football League in total defense last year, it takes quite a bit of intestinal fortitude to count on the New England Patriots as a starter in fantasy football leagues.
However, the Patriots' tendency to force teams into shootouts also forces opposing quarterbacks to make errant throws, as evidenced by New England's league-leading 25 interceptions a season ago.
That, coupled with a pass rush that racked up 36 sacks in 2011, at least makes the Patriots worthy of fantasy consideration as a "matchup" play.
The Seattle Seahawks improved significantly on defense last year, and by season's end a team that ranked a woeful 27th in the NFL in 2010 had cracked the top 10 in total defense.
The Seahawks also cracked the top 10 defensive units in fantasy points scored in 2011, and while it may not be advisable to rely on them week in and week out, the Seahawks are absolutely worth a look when the matchup is right.
Quarterback Tim Tebow may have gotten most of the credit for the Denver Broncos' surprising playoff run last year, but in fact many of the kudos should have gone to the Denver defense, which played much better football down the stretch.
The loss of starting defensive end Jason Hunter to injury, linebacker D.J. Williams to suspension and safety Brian Dawkins to retirement are all significant question marks however, leaving the Broncos as more of a matchup play than weekly fantasy starter.
The New York Jets have a defense that is greater than the sum of its' parts, as although the team doesn't feature any "star" players outside of cornerback Darrelle Revis, Gang Green still ranked in the top five in total defense a season ago.
However, that ranking didn't really translate to fantasy production, especially on a weekly basis, and the Jets' relative lack of big plays (especially sacks) and inconsistency from a fantasy standpoint robs them of a lot of their luster in fantasy leagues.
The Cincinnati Bengals were one of the surprise teams in the National Football League a season ago, due in no small part to a defense that ranked seventh in total yards allowed and ninth in scoring defense.
The Bengals were also fifth in the league in sacks and sixth in fumble recoveries, which was enough to make them a top 12 fantasy defense in 2011 and worthy of consideration as a matchup play in 2012.