Every off-season, as teams reconstruct their rosters, we hear analysts and fans talk about replacing last year’s players. This rose to prominence this off-season, when the Yankees faced losing three of their more popular players. As the off-season progressed, many wondered how the Yankees would replace the production of Hideki Matsui and Johnny Damon. The eventual answers, Nick Johnson and Curtis Granderson, did not satisfy everyone. I think, however, that this misses the point of roster construction.
Player production fluctuates from year to year. Some players on a given roster will improve their numbers over the previous year, and some will decline. Even established players will see varying levels of production to some degree. Players do have bad years occasionally, just as they have career years. They benefit from good luck and fall victim to bad luck. Injuries can shorten seasons and hamper production. As players exit their primes their skills erode, and as players enter their primes their skills take full shape.
At designated hitter, Nick Johnson takes Matsui’s place. Based on their 2009 numbers, this is an almost one-for-one replacement. Johnson’s wOBA was just .005 lower than Matsui’s, and they had identical WAR values. This indicates that Johnson will replace Matsui’s production, but it completely ignores the year-to-year fluctuation. Both players missed much of 2008 with injuries, but both played all of 2009 — and Johnson actually accumulated 46 more plate appearances. The bet the Yankees have made is that Johnson’s non-specific injury history is a better bet than Matsui’s balky knees. Add in Johnson’s age and you might understand why the Yankees bet on the younger player.
In the outfield, Curtis Granderson replaces Johnny Damon. While Damon certainly had a better 2009 season, it does not necessarily indicate that he’ll perform better than Granderson in 2010. Granderson had a particularly bad season compared to his previous two, and could easily bounce back to be a highly productive player. Meanwhile, Damon, seven years Graderson’s senior, ended the season in a horrible slump, perhaps an indicator of his age. We don’t know any of this for sure, which makes it difficult to gauge whether one will adequately replace the other.
Even then, we have to determine whether each returning player will replace his production from the year prior. Will Jorge Posada replace Jorge Posada? Jeter for Jeter? Both had particularly good years, but both are exiting or have exited the primes of their careers. There’s a chance, though I’m not sure how great, that their production declines this season. This applies to Matsui and Damon as well. We’ve heard many people — reporters, fans, and analysts alike — talk about Johnson and Granderson replacing Matsui and Damon, as if it’s a lock that Matsui and Damon reproduce their 2009 seasons. The same applies to them as to Jeter and Posada.
During the season we see the trees. We can observe and measure how each player has contributed to the team. In the off-season, all we can really look at is the forest. Does the team have a solid lineup? Does its rotation feature a number of out-generating pitchers? We can drill down even further, looking at what types of hitters and pitchers compose the team. But it’s tough to tell, from an individual player standpoint, how the team stacks up to the previous year’s. There’s just too much variation to account for. This is not to say that we can’t predict and project how players will produce. It’s that we tend to focus on the replacements while ignoring the returning players.
Every team changes between seasons. Not only do they add and subtract players who will perform differently than their counterparts, but their returning players will not necessarily reproduce their previous season. Roster construction talk often involves the idea of replacing production, but if we can’t determine how a player will replace his own production, I’m not sure it’s fair to talk about a new player replacing that of an old one. That is, it’s fine for casual debate, but I don’t think the Yankees use that when building their teams. They just want the best possible construction, regardless of who replaces whom.