I've gotten quite a few questions about this, so I'm happy to explain. That's right, I'm talking about postseason eligibility.
Here's the short answer, the one that everyone wants: Yes, Jacoby Ellsbury is potentially eligible for the postseason roster. I'll explain. Or, rather, I'll let Red Sox director of baseball operations Brian O'Halloran explain.
"The position-player-for-position-player / pitcher-for-pitcher requirement is indeed now gone for substitutions prior to a series," O'Halloran wrote in an e-mail. "However, teams now are allowed to substitute for an injured player during a series. Such in-series substitutions are position-player-for-position-player / pitcher-for-pitcher, and the injured player cannot be active for the remainder of that series or the next series. Those substitutions also require MLB approval.
"The way substitutions (before a series) work in general is as follows: each team's initial pool of eligible players is the 25 players on its active roster at midnight on 8/31 plus any players on the 15-day DL, 60-day DL, suspended list, bereavement list, etc. So we have 28 players in this pool (25 plus Donnelly, Clement, and Mirabelli, all of whom were on the DL on 8/31). Any player in a team's pool who is injured when a given series begins can be substituted for. So if Mirabelli is healthy at that time he will not be eligible to be substituted for, as an example. But if any player of the 28 eligible guys is hurt at the beginning of a series, we could substitute for him. For example, with Donnelly being out for the year, we can substitute any player who was in our organization on Aug. 31 for Brendan. This substitute could be a pitcher or position player, and does not necessarily have to have been a September callup."
So there's your answer. Ellsbury could be in, even though he wasn't on the 25-man roster as of Aug. 31.