Once the rules were changed to prevent catchers from blocking the plate, it was inevitable there would be some interpretation problems. Baseball's been played one way for more than a hundred years and now everyone has to learn a new way. It's not an easy adjustment.
Here's what rule 7.13 says:
Unless the catcher is in possession of the ball, the catcher cannot block the pathway of the runner as he is attempting to score. If, in the judgment of the Umpire, the catcher, without possession of the ball, blocks the pathway of the runner, the Umpire shall call or signal the runner safe.
In determining whether a runner deviated from his pathway in order to initiate a collision, the Umpire will consider whether the runner made an effort to touch the plate, and whether he lowered his shoulders or pushed through with his hands, elbows or arms when veering toward the catcher. The rule that will be in effect in 2014 does not mandate that the runner always slide or that the catcher can never block the plate. However, runners who slide, and catchers who provide the runner with a lane to reach the plate, will never be found to be in violation of the new rule. Beginning immediately, Clubs will be required to train their runners to slide and their catchers to provide the runner with a pathway to reach the plate at all levels in their organizations.
I guess it was overturned because Martin had his foot on the plate before being in possession of the ball? That seems ridiculous on a bang-bang play like that.
The Pirates are getting clobbered (box score), so the play is mostly inconsequental, but this is something MLB needs to revise. I totally understand eliminating unnecessary home plate collisions. But now catchers can't stand on the plate for a force out? Come on now.