Concern has been mounting over Brian Roberts' back as he has been held out of several practices. He has downplayed the severity of this injury. This typically would not be of much concern were it not for two issues:
- Historically, second basemen fall apart in their early thirties.
- Last year, Roberts was injured during Spring Training and similarly played down concerns over an injury that wound up shutting him down for the majority of the season.
After the jump, a run through of graphs showing what can be expected in terms of plate appearances, WAR, chance of being an average player, and chance of remaining in the Majors.
The following graph shows the average number of plate appearances for each age class, the median, and the 25th/75th percentiles:
The next graph, goes beyond looking at playing time and focuses on performance. Instead of plate appearances, Wins Above Replacement (WAR) is used to describe the population:
as I mentioned when the extension took place in 2009).
This final graph describes this population of second basemen by showing what percentage of them were above average and how many of them remained in the majors.
I ran through several regression trying to determine if I could predict Roberts collapse, but there does not seem to be a shared trait or set of trait that dictate an evaporation of ability within this subset of second basemen. The only trait that seemed to be unique to second basemen who were successful deep into their thirties was having an above average defensive WAR as Baseball Reference calculates it. 3 of 7 players who had a positive WAR during their Age 27 to 31 seasons had a WAR above 10. In the group who registered below average defense, only Ray Durham retained his success. Brian Roberts, if included in this group, had the worse defense WAR with -22. This is an awful small sample size, but it suggests not a good future for Roberts.
This really should not have been a surprise.