Longwell’s major limitation is his inability to produce touchbacks on kickoffs. In 2011, he ranked 28th in the NFL with just 19 kickoffs, and he ranked 34th by forcing touchbacks on just 24.7 percent of his kicks (in part because of this, the Vikings ranked 31st in the NFL in average opponent starting position, according to Football Outsiders' drive stats. Vikings opponents started the average drive at the 31-yard line, while the 49ers defense/special teams led the NFL by forcing opponents to start each drive, on average, at their own 24-yard line).
That might not seem very important, but according to people who are a lot smarter than me, it is. According to an article on a website called Advanced NFL Stats, touchbacks are a lot more valuable than you might imagine. The article is from 2009 and is therefore somewhat outdated, but the findings remain valid today. You can see all the nerdy details here if you’d like, but the highlights of the research done by Brian Burke at Advanced NFL Stats are these:
Using a concept called Expected Points, Burke concludes that a touchback is worth the rough equivalent of half a sack (to drastically oversimplify things, this means that forcing a team to start out at their own 20-yard line twice in a game has roughly the same negative effect on the expected points that team’s offense will score as does sacking the quarterback once).
The average field position for non-touchback kickoffs is the 32-yard line. Therefore, each touchback saves 12 yards of field position, which results in the opposing offense having to attain one more first down than they would have otherwise in order to get into scoring position. According to Burke, “the average first down conversion rate in the NFL is 67%, so a touchback turns a TD drive into a FG drive or a FG drive into a punt 33% of the time.”
For the sake of argument, let’s assume Walsh makes the team as a kickoff specialist, or just beats Longwell out for all of the place-kicking duties, and is able to boot 33 touchbacks in 2012, which was the league average for the top 32 kickers in 2011. According to Advanced NFL Stats’ Expected Points, Walsh’s addition, purely in terms of field position and allowing fewer points, would be the equivalent of the Vikings having added a defensive player who produces 6.5 sacks this season. And when you consider that the top 10 kickers in 2011 all booted at least 40 touchbacks, Walsh’s impact could be even greater if his leg proves significantly stronger than Longwell’s.
It’s a fancy way of saying what should be obvious – starting field position does matter in the NFL, and the ability of a kicker to produce touchbacks and prevent long kickoff returns is a factor in winning and losing games.