Sunday, August 16, 2009
Poz getting it wrong again (or at least overstating his case)
Poz talks about Betancourt again. He cites his 2009 Dewan plus/minus and his UZR to make the case that he is a terrible defender which irks him because Dayton Moore and some of Betancourt’s new teammates (namely Bloomquist) think that he is a very good defender. Poz also says that if you watch him play and you look at his error totals (2) in the last 28 games, you might think he is around an average defender. Once gain, he is complaining bitterly about the signing.
He makes some mistakes in the article, and again, I don’t think he should be making these kinds of mistakes if he is to be revered as much as he is by some sabermetric folk.
From the Poz article:
John Dewan and his people at Baseball Info Solutions have come up with a way to measure defense. What they do, using video technology, is chart every single batted ball on a computer. And then, after entering all the data (how fast the ball’s going, the direction, the height, etc.), they determine how often that exact ball is turned into an out. For instance, a hard ground ball 6 inches to the right of third base — how often does the third baseman come up with that play and throw out the runner. How about a high chopping ground ball that is just over the pitcher’s glove? How about a slicing line drive that would hit the chalk in right field?
He is really overstating the precision with which the data is recorded and I think he knows that, or at least should. There is no way that they can differentiate between a ball hit 6 inches from the base line and 3 feet from the base line. And there is NO category that I am aware of that is a “high chopping ground ball just over the pitcher’s glove.” Come on!
Which is one reason why there is so much measurement error in these metrics in the short run. A high chopping ground ball over the pitchers mound (that could easily be fielded by either the SS or 2B) could just as easily have been a ground skinner up the middle that no one could possibly have fielded. They could easily fall into the same bucket, in which case, the fielder who catches the first one will be over compensated on that ball and both the SS and 2B will be overly penalized on the second one. In the long run all of these things will even out, but in the short run, they create all kinds of problems due to measurement error and even bias.
According to the system, an average shortstop — not a good one, mind you, just an average one — would have made 15 more plays than Betancourt did in his first month.
Or another way: If you stretched that out over, say, 150 games, the system says he would make EIGHTY-THREE fewer plays than the average shortstop. It’s unheard of. It’s lunacy. Nobody compares.
No, no, no and no! That does NOT mean that he would be 83 plays below average after 150 games any more than if Adam Everett was -1 play after one game, that would mean that he would be 150 plays below average after 150 games! I HATE when people do this!
If Betancourt is -15 plays so far, it is likely that he was somewhat bad on defense, but worse than his true talent, and it is also likely that there is measurement error in that number such that he was probably only half as bad as that number. That is why if all we knew was that a player was -15 plays after 100 games, we would call his true talent like -8 per 150 or something like that, which is bad but not horrible.
And if Poz really wants to talk about how bad of a SS that KC got in the trade, he needs to STOP quoting numbers from 100 games only. Again, he knows that. His total career UZR at SS is -7.2 per 150. If we weight the individual years, it is probably -10 or -11, which is not good, but let’s not mislead people by quoting things like, “That’s 83 plays below average (per season)...”


If I had a dime for every time someone argued against the usefulness of fielding stats by stating that it’s physically impossible for a player to be 83 plays below average, i’d be rich.
Hyperbole can actually get in the way of an argument.
You’re dead on righteous to argue that measurement error and true talent must always be an important part of the prism one uses to interpret any metric.