I think 20 TDs is such a rare occurrence that it's difficult to predict it happening again
There have been 20 instances of 20+ RRTD for RBs since 1970- but 11 of those have come since 2000, and Williams was averaging 11 more y/g in 09 than he did in 08 before his injury (not counting game 13) which is worth 2.5 more TDs. There have been 43 instances of 17+ TDs since 1970 with 21 coming since 2000 and 28 since 1995- the upward trend in scoring has lead to more big individual years for RBs even with all the extra passing going on. If there are 32 RB years per year then over the last 10 you have ~6.5% chance of a 17+ TD season as a starting RB. Of note - that list of 21 RBs with 17+ TDs since 2000 Ahman Greene, Clinton Portis, Ricky Williams, Adrian Peterson and Michael Turner along with Deangelo did not/have not repeated- that is 3 RBs out of 12 who have basically finished their careers without duplicating, 6 who have duplicated and 3 who have done it for the first time the past 2 years and will have opportunities to duplicate. Once you find yourself in a situation where you are able to get 17 TDs or more there is a pretty good chance of repeating.
I'm not sure what to make of this post.You start out by stating that 20 times a RB has rushed/received 20+ TDs in a season since 1970, but that over half of those (11) have come in the last decade. This is an important point, because as you have noted, there's been a recent upward trend in TDs by RBs.Then you say that Williams was averaging 11 more yards per game in 2009 (than 2008), which is worth 2.5 more TDs? What is that supposed to mean? Are you talking about fantasy points? If so, that's not really relevant. The discussion is about the potential for Williams to put up the type of season he put up in '08, and the 20 TDs were a big part of that. There's been little debate about Williams' ability to put up yards or a high YPC. Repeating the 20 TDs is the issue.Then, for some reason, you decide to start using 17 TDs instead of 20. 17 TDs isn't 20. Would it be more likely for Williams to rush for more yards and less TDs? Yes, but that really isn't the point, is it? The point of the post you quoted was that 20 TDs is a rare occurence. Not that the FF point of 20 TDs is a rare occurence. Therefore, suggesting that Williams can get more yards and make up for fewer TDs isn't really germane.As to the issue of 20 rush/receiving TDs:In the last decade, 11 times a RB has accumulated a total of 20+ rush/rec TDs. This has been done by 7 different RBs. Tomlinson did it twice, Alexander did it twice, Holmes did it twice, Faulk did it twice, with Johnson, Green, and Williams accomplishing the feat once each.To be fair, you almost have to discount Faulk from this list. In the 2 seasons where he scored 20 TDs (2000 & 2001), he only had 253 and 260 carries. However, he had 81 & 83 receptions in those seasons, as well as 8 & 9 TDs. In essence, Faulk was a freak, serving not only as a RB, but also as a WR, in order to get his 20+ TDs.That leaves LT, Alexander, and Holmes as repeating 20+ TD RBs, with Johnson, Green, and Williams as non-repeating.So, you could look at that list & say "A RB who scores 20+ TD in a season has a 50% chance in repeating the feat," but that would be foolish for several reasons.First, and foremost, the sample size is too small. Second, if you look at the situations, those other RBs averaged over 388 touches/season in the years they scored 20+ TDs. This makes sense, because it takes a large amount of touches to have the opportunity to score 20+ TDs. DeAngelo Williams only had 296 touches in his 20 TD season.For him to reach 388 touches/season, he'd have to get 6 more touches a game. Could it happen? Yes. Is it likely? No.