It's been an awful couple of weeks for baseball injuries. On the young season, we've already seen stars Josh Hamilton, Joe Mauer, Evan Longoria and Ryan Zimmerman go on the disabled list. You can't really replace the production of players on that level, but some of them are more irreplaceable than others.
When determining the most valuable players in baseball, an ever-increasing number of statistical tools are now at our disposal. The most straightforward of these is wins above replacement (WAR). Yet analysis of which players are most valuable often seems to stop at the water's edge of that player's value in a vacuum. In reality, how valuable a player is to his team is determined not just by his own production, but also by how much more production he provides than his team's Plan B at the position. Yes, this means of evaluating penalizes players who play for deep teams, but it is a reality.
If a player has a WAR of 6.0 in a season, and his backup is negative -2.0, that player is more valuable to his team than another player with a WAR of 9.0 whose backup is worth 4.0.
That's why, on this list of the most irreplaceable players in baseball, you won't see Longoria. The estimated full-season dropoff from him to backup Sean Rodriguez is roughly 3.0. That's a lot, but it's not among the five highest in baseball. Hamilton was a big loss for the Rangers this week, but Texas doesn't lose nearly as much as you'd think. Thanks to David Murphy, one of the best fourth outfielders in the game, the dropoff is around 3-4 wins over a full season.
Let's take a closer look at the five most irreplaceable position players in baseball, whose misfortune would provide the most doom when you factor in the quality of the players' backup: