Let's take a look at what happens when Brett Favre changes teams. Since he became the superstar we all know, he's only changed teams once not including his recent return to the NFC North. This will give us a very small sample size, so we can't really rely fully on it, but it gives us an idea of what can happen. In 2008 Favre left Green Bay and went to the NY. Let's take a took at how that affected the RBs of the Packers and Jets.

In 2007, Favre's last year with in Green Bay, the Packers had a hole at RB through their first six games, but Ryan Grant emerged as the starter after the Bye week. In their final 10 games, Grant had 182 carries for 929 yards and eight rushing TDs. He also had 25 receptions for 121 yards. Pro-rated for an entire season, that's 291 carries for 1486 yards and 13 TDs, along with 40 receptions for 194 yards, for a grand total of 245 fantasy points. In 2008, Grant's first year without Favre, Grant played all 16 games and had 312 carries for 1203 yards and four TDs, as well as 18 receptions for 116 yards and one TD. That netted him 161 fantasy points.

That is a big difference. Grant was slowed by some bumps and bruises, and the defense had a poor year giving the offense less time on the field and and putting them in tough positions usually trailing on the scoreboard, but 80 fantasy points is a lot. Another interesting number is his yards per carry. With Favre he was gaining 5.09 yards per carry, while he only gained 3.86 yards per carry without Favre. Oddly enough, his yards per reception increased when Favre left town, from 4.9 to 6.44.

Now let's look at Favre's impact on the Jets' running game. The Jets had Thomas Jones as their feature back in 2007 and 2008, so we can compare his two seasons as we did for Grant. Jones played 16 games in both seasons with the Jets, so we can compare them equally. Without Favre Jones rushed 310 times for 1119 yards and one TD, and added 28 receptions for 217 yards and another TD, for 144 fantasy points. When Favre came to town Jones rushed 290 times for 1312 yards and 13 TDs, along with 36 receptions for 207 yards and two more TDs, which resulted in 241 fantasy points.

Jones increased his fantasy scoring by almost 100 points with the addition of Favre while Grant's scoring dropped over 80 points when Favre left. That makes a pretty strong argument. Let's also look at Jones' averages when he got the ball. Before Favre showed up Jones averaged 3.61 yards per carry and that jumped to 4.52 yards per carry once Favre was his signal caller. Just as happened with Grant, Jones' average yards per reception dropped with Favre, from 7.75 to 5.75.

In both cases, with Grant and Jones, their fantasy production was 34% and 40% higher with Favre. Those are some pretty big numbers. Add in the difference in their rushing yards per carry, 24% and 20% respectively, and the case is made pretty strongly. You might wonder what's going on with the average yards per reception dropping with Favre sharing the backfield, but that could be because opposing defenses are expecting the pass so they are in better position to defend it.

One argument that could be made to explain the numbers could be the ages of the RBs, but this actually backfires as Thomas Jones' 8th season was pre-Favre and his 9th season saw his best performance of his career, something that normally doesn't happen for 9th year RBs, they are usually declining by then. But in his 9th year, his only year with Favre, Jones had his only double digit TD season, and had his second best season in terms of both rushing yards and yards per carry. On the flip side, Grant is a young RB and it would be expected that his second season would be better than his first, but his second season was his Favre-less season, and saw worse production than his rookie year.

Perhaps one could argue that there were considerable changes to the Packers and Jets between 2007 and 2008. Excluding the change at QB, there weren't. Both teams returned their WRs and RBs and the majority of their offensive lines. The Jets got better in the win column as the Packers got worse, but that could be a direct result of Favre himself, and his apparent affect on the running game.

So how does this affect Adrian Peterson? Well, if we take rough improvement numbers from the two examples above, his fantasy production would increase by 34% and 40%. He scored 248 fantasy points last year, so will he score between 332 and 347 fantasy points this year? That is highly unlikely, but an increase in fantasy points is certainly possible. His 1760 yards and 10 TDs were very impressive, but are far from surmountable. According to increases in yards per carry Peterson could average between 5.76 and 5.95 yards per carry with Favre. This is also unlikely, but it is reasonable to think he could increase his 4.8 yards per carry from 2008.