The word “move” is used in the context of an offseason to denote any number of varying transaction types. A trade is a move. A free-agent signing is a move. A player being designated for assignment is a move, or claimed off waivers, or sold to Japan. Players coming and going from rosters are the moves of the winter, and they’re the means by which the public tends to evaluate a team’s offseason.
The calculus for the outlook of the upcoming season is constantly changing throughout the offseason as these myriad moves transpire. When a team signs a star free-agent pitcher, we know that that team is several wins better than they were the day before. When a rebuilding club trades away its slugger in the final year of his contract for prospects, we understand that they’ve dropped a couple wins for the upcoming season.
But there’s another sort of move that happens during the offseason that’s more subtle, and it, too, changes the calculus of the upcoming season, though it often seems to be overlooked. We spend so much time and effort analyzing who “won or lost” the offseason that it’s easy to forget how much change should be expected from a team’s returning players. The Rangers didn’t go out and sign Yu Darvish this offseason, but he is expected to be a valuable addition to this year’s roster, an extra four or so wins added without any kind of traditional offseason move. Without doing anything, the Rangers rotation looks significantly better than it did at the end of last year.
Six years ago, Dave Cameron wrote a short post on this site titled 2009 Is Not a Constant. I recommend you read it, and sub in “2015” for “2009” when applicable, but here’s a relevant passage anyway:
We all know about career years and how you have to expect regression after a player does something way outside the ordinary, but regression doesn’t just serve to bring players back to earth after a big year.
Regression “fixes” a lot of problem spots from the prior year, even if the team doesn’t make a serious effort to change out players. The Royals got a .253 wOBA out of their shortstops a year ago. I don’t care how bad you think Yuniesky Betancourt is, you have to expect that number to be higher this year. They didn’t do anything to improve their shortstop position this winter, but the level of production they got from the position in 2009 is not their expected level of production for 2010.
You cannot just look at a team’s prior year won loss record – or even their pythagorean record – make some adjustments for the off-season transactions, and presume that’s a good enough estimator of true talent for the 2010 team.