Just by watching the Vikings play this season you can see that their defense is executing better. The improvement has been apparent both on the field and on the scoreboard. Undoubtedly, Christian Ponder's game management, Percy Harvin's game-changing plays, and Blair Walsh's leg have all been major contributors to their 4-1 start. But more than any other factor, their strong defense has been responsible for their first-place standing.

Putting your finger on exactly why the Vikings are playing better defensively is harder to do. They aren't pressuring the quarterback quite as well as they did last season when they tied for the NFL lead in sacks and Jared Allen threatened the single-season sack record. They aren't returning turnovers for touchdowns a la the Chicago Bears, with whom they share the top spot in the NFC North. They are permitting opponents to convert on third downs at a 44.2 percent rate – the exact same rate at last season, ranking among the bottom third of defenses in that department. Even so, they are definitely playing better. As head coach Leslie Frazier put it Monday during his press conference, "They're playing with great energy, you can see the guys are playing with confidence, they're in the spots they should be, and when they're in those spots they're able to make some plays for us." In other words, they're not making highlight-reel plays, but they're doing what they are supposed to do. They are in their spots and making plays when they need to do so. They are executing. That alone is a significant step in the right direction. Exactly how much better have the Vikings played through five games? It's admittedly a small sample size, but the first five games of this season compare quite favorably to 2011 across the board. The noted pigskin mavens at ProFootballFocus.com rank the Vikings as having the third-best defense in the NFL thus far this season, compared to 14th overall last year. Here are a number of more specific areas that might make their improvement easier to understand: Vikings defensive comparison 2011 NFL Rank 2012 NFL Rank Points allowed per game 28.1 31 15.8 6 Yards allowed per game 358.2 21 304.2 7 Pass yards allowed per game 251.2 26 225.6 14 Rush yards allowed per game 107 11 78.6 6 QB rating allowed 107.6 32 84.6 12 Completion % allowed 68.2 31 61.8 14 Yards per rushing attempt 3.9 6 3.2 2 Passes defended 50 31 32 3 As you can see from the table above, they remain rock solid against the run, truly one of the five or 10-best run defenses in the league. They have not allowed any run longer than 15 yards this season. No other team in the league can make such a claim. However, their improvement against the pass (so far) has been the biggest differentiator. Look at the QB rating allowed stat. In 2011, their 107.6 mark was the second-highest allowed in the history of the NFL. It was like facing Tom Brady (105.6 rating in 2011) or Drew Brees (110.6) every week. They've got that number down into the realm of mere mortal quarterbacks this season – and in a passing league, that's pretty important. Chad Greenway is playing like a Pro Bowler and ranks second in the NFL with 53 tackles thus far. If I had to pick a Vikings defensive MVP through five games, he'd be my choice. However, fellow veterans Kevin Williams and Antoine Winfield are looking more and more like they did three years ago. That definitely helps. As does the emergence of Jasper Brinkley at linebacker and the improved play of the secondary. Oh the secondary -- so horrible last season and so pleasantly surprising this season! The stats tell the story. But the story has its new characters. Aside from foolishly putting his hands on an official this past Sunday and earning an ejection, rookie safety Harrison Smith has provided the secondary something it's lacked in, well, an awful long time: a hard-hitting intimidator. It also helps, as Frazier alluded to, he's been in the right place at the right time and he's making plays -- as evidenced by his six passes defensed. The same should be said for fellow rookie, cornerback Josh Robinson. He's probably been the most pleasant surprise. We knew he could run. We knew he had ball skills. His tackling has really stood out, though. And maybe it's as simple as that. Be where you are supposed to be and tackle. The Vikings have done that so far this season, with rare exception. Bo Mitchell is the VP of Content at SportsData and co-host of the Fantasy Football Weekly radio show on KFAN 100.3 FM. You can follow Bo on Twitter at @Bo_Mitchell