I mostly ignore the innumerable NFL pre-season stories. Most of them are empty blather by journalists charged with filling more pages than there are interesting stories. Even for the minority of substantive stories, come on: This is baseball season. We have actual pennant races to follow! It’s not like baseball’s pre-season, which takes place while no other major sports are playing. 
I was surprised to stumble across an exception: an NFL pre-season story I will follow with interest. It is the story of Jarryd Hayne. He is a Rugby League player from Australia. He isn’t just any random Rugby player. He is one of the best in the world, and has the awards to show it. Yet he recently signed with the Santa Clara 49ers as a running back.
Much has been made of the money aspect of this. He was on the verge of signing a record-breaking Rugby contract for $6 million for three years. Sure, those are Australian dollars, but this still comes out to over $4 million American. The 49ers are paying him about a third that, assuming he makes the team. His talk is all about meeting the challenge of the NFL, and I see no reason to doubt this. On the other hand, the financial possibilities of the NFL clearly are substantially greater, given the absurdly low number of American professional sports standards of that record-breaking contract he turned down.
What interests me, though, is the mere possibility of a top-level athlete making the transition from one sport to another. This is virtually (?–Perhaps entirely) unheard of. There have been athletes who have played multiple sports before: Bo Jackson and Deion Sanders are examples within living memory. But they played both sports all along.
This is something different: going from one sport to a different one as an adult. This history of athletes trying this is not promising. The most notable attempt was Michael Jordan’s ill-starred foray into professional baseball. He never got past AA-level in the minors, where he batted a measly .202. I don’t conclude from this that baseball is more difficult than basketball, but that the skill sets are different, and specialization matters. I have no doubt that had he specialized in baseball at an early age, he would have been an excellent player. But he didn’t, and therefore wasn’t.
Another potential transition, and one that seems more natural, is between cricket and baseball. E. T. Smith, a professional cricketer who played for Kent County, went to the Mets spring training, and wrote a book about it, Playing Hard Ball. (It is a good book, but be forewarned that it was aimed primarily at British readers. He occasionally descends into Cricket Gibberish without providing any translation.) He was there on a press pass, but the baseball guys knew his background. He also knew that baseball players made a bunch more money than cricketers. (This isn’t necessarily true today, but this was about twenty years ago, before the India Premier League.) Reading between the lines, both sides had a tickle in the back of their heads that something more substantial might come of this. It didn’t. While both sports involve using a bat to hit a ball, the devil is in the details. The deliveries and swings are different enough that the skill doesn’t translate, and the learned habits may indeed be a positive impediment. There is the occasional ballplayer from Australia or the Caribbean who grew up playing both games, but an adult can’t just wake up one morning and decide to switch games.
This is consistent with 19th century experience. Cricket once was pretty mainstream in America. Baseball and cricket teams often played against one another through the 1870s. You even find top professional baseball clubs doing this occasionally. The usual result was that the baseball club won when they played baseball, and the cricket club won when they played cricket. There had to be a wide disparity of athletic ability before this changed.
About the only noticeable exception I know of is the trendlet of some years ago to recruit soccer players as NFL kickers. I associate this with Tom Landry, though I imagine he wasn’t the only one. This, while interesting, is a marginal case. I don’t jump on the “kickers aren’t real football players” bandwagon, but their skill set is distinct from the other players. Running back is another matter.
This is why I am interested in Hayne: can he buck the trend and make the transition? I think he might. Rugby and American football are closely related games. They were the same game originally, but the Americans had trouble figuring out how to make the Rugby rules work. (This is not a criticism: there were implicit assumptions that are hard to work out from the text alone.) They started fiddling with the rules around 1880, with modern American football the eventual result. Among the various American football positions, running back would seem the least changed from its Rugby antecedent. The essence of advancing the ball in Rugby is to run with the ball while a bunch of guys are trying to tackle you. That is pretty much the essence of the running back, too. There are differences, of course: helmets and padding are the obvious ones, while knowing where to run is non-trivial.
We’ll see, but I would think that this transition is doable. Hayne has gotten off to a good start. He had a 53 yard run against the Texans. He got a good block and broke past one guy in the backfield. This is just pre-season, of course. But it’s not as if I could get a 53 inch run under those circumstances. I am staying tuned.
 Suck on it, basketball and hockey fans!
 Not to be confused with the Landover Redskins. Don’t even get me started on the Los Angeles Angels of Anaheim.
[Edited to put back in the paragraph breaks that had mysteriously disappeared.]