Originally conceived as a way to get Departed and Other Guys reunions happening concurrently, to make most efficient use of our dwindling Mark Wahlberg supplies, Three Mississippi (previously Turkey Bowl) was to star Wahlberg, Will Ferrell, and Alec Baldwin in a film about childish middle-aged men competing in an annual tackle football game. Now, the Wahlberg part is being given to Adam Sandler, casting him as rival to his fellow SNL breakout and son to Baldwin, thereby making his relationship with his scoutmaster that much more uncomfortable.
Though most would have accepted "because a Sandler/Ferrell film will obviously make a lot more money" as rationale for the change, Vulture has gone into the details of the decision, which basically had to do with scheduling. Wahlberg has committed to shooting Peter Berg's Battleship follow-up, the similarly-naval themed Lone Survivor, this fall; at the same time, Ferrell and Three Mississippi's would-be director Adam McKay unexpectedly got the green light on shooting Anchorman 2 early next year, leaving this fall as the only time Ferrell is available to shoot, thus forcing Wahlberg out of the film and leading someone to say, "Well, if you can't get Mark Wahlberg, Adam Sandler is essentially the same guy, right?" The Anchorman thing also forced McKay out of the director's seat, and now Sandler's That's My Boy director, Sean Anders, is taking over.
Sandler has not yet officially signed on to the project, but just go ahead and try and imagine him turning down a role as a suburban father horsing around with fellow SNL alumni. So yeah, Sandler and Ferrell are going to be in a comedy together. How is that only just now happening?