In all the stories explaining in detail why "obstruction" was called on Boston Red Sox third base man Will Middlebrooks last night so as to award a run, and the game, to the St. Louis Cardinals, everybody continues to miss the most important point: Middlebrooks not only was not obstructing the ordinary basepath (meaning the baseline or three feet to the outside of it) of runner Allen Craig, but he wasn't even obstructing the bizarrely skewed basepath established by Craig after Craig got up from the base, looked back at the ball, and took a step back into the field, in the general direction of second base.
First things first: The key factor here is whether the runner's "basepath" was obstructed. There are several other ancillary considerations, but none of them even come into play if the basepath wasn't obstructed. Just because a runner trips over a fielder doesn't mean the runner officially was "obstructed"; for the call to be made, his own path from starting point to the next base must have been obstructed.
Well, first, if Craig had not inadvertently stepped back into the field of play upon arising from the missed catch/tag, his starting point would have been third base, not two feet inside the line. He did not end up inside the line because of the collision, but because of his own step upon arising -- a step taken not while trying to get to home, but while trying to locate the ball. So there is a question, to start with, as to where the beginning point of the path is to be properly determined -- because, according to the rules (I read and re-read them extensively last night again AFTER my initial post on the matter; I hope later today to copy and past the relevant rule to which I refer, but my computer is being balky with attachments right now), the basepath is determined from the point where the runner is as a result of the missed tag. I think the starting point should have been on third base or maybe six inches inside it, not the two feet inside it after Craig took his confused sideways step while looking back for the ball.
But even if you grant him the two feet inside the line to start with, the most important point is that he then did not start running toward home; instead, he was still (as my wife would say) caterwampus -- running askew -- when he tried to start running. In other words, the angle he took, which is what led him to trip over Middlebrooks, was not toward home, but at a weird angle that, if he followed it, would have taken him closer to the pitcher's mound than to home. If he had turned straight toward home from his spot two feet inside the baseline, he might barely have grazed Middlebrooks' upturned legs, but almost certainly could have avoided tripping.
This photo -- here -- tells the tale, although another photo I saw, unlinkable, from a wider angle, shows it even more definitively. You will see that Craig has no idea where he is going, but that he is angled well inside the line, not towards home plate. In fact, when you watch the video, you will see the same thing, even more starkly, although you have to watch closely and maybe do some stop-action work. Craig might have the right to establish his own "path," but he must follow the path -- a straight line from start to finish -- that he has established, not a long and winding path of his own choosing.
Aside from that, while the concept of "intent" does not, by the rules, play into "obstruction," for there to be obstruction there must be an "act" by the fielder. The act might be, as as example in the rules states, remaining prone on the ground unnecessarily -- but if one is on the ground and cannot get out of the way, then one has committed no act of obstruction. In this case, oddly enough, the apparently reflexive bouncing up of Middlebrooks' legs actually acted to make a cleaner path, not a more difficult one, for Craig to have run to home, if Craig had run straight rather than sideways -- because the legs up in the air had the effect of clearing an extra 18 inches or so of space along the baseline for Craig to run had Craig run in a straight line.
I could go on, but I maintain my contention that the call was wrong. In the spur of the moment, based on how the rulebok now reads, I think it is more than understandable why the umps made the call they did. But upon very careful further review, it was not the right call.