We have been through this, and I've explained why "the law of large numbers" isn't applicable, when you don't know the accuracy of the data you're inputing. As for "that didn't happen," From Mitchel Lichtman ("MGL" on various chat boards, the man responsible for UZR): People often say something like, “Well, he had a +10 UZR last year, which means that he actually played well, even though he might be an average or even below average defender.” For example, Jeter had a very nice UZR in 2009, a decent one in 2008, and some terrible ones for many years prior to that. So, he is a perfect example of a below-average defender who played excellent defense last year and pretty good defense the year before, right? Well, maybe and maybe not. A player’s UZR does not necessarily tell you how he actually played just as it does not necessarily tell you what his true talent is. That is a very important point. It is not like we pulled a coin from our pocket and flipped it 100 times and came up with 60 heads (which is entirely possible, even though we presumably have a fair coin). In that case, we can safely say that, yes, we did in fact get 60 heads (Jeter did in fact play well last year), even though we know that the true heads percentage of our coin is around 50% (Jeter’s true talent at SS is very likely below-average). UZR does not work that way. Why is that?That is because it is not measuring something that is categorized, like a coin flip which either comes up heads or tails, or BA, whereby a player either gets a hit or he doesn’t, or even simple Zone Rating, where a fielder either fields a ball within his zone or he doesn’t. And here is more from the same kind of post UZR tries to record a player’s likely true talent and estimate his future performance based on the nuances of the batted ball and the player’s response to those nuances. It is not trying to capture exactly what happens on the field according to some arbitrary categories, like most of the offensive metrics (which make no distinction between a lucky ground ball bleeder through the “5-hole” or a clean, line drive base hit to the outfield), even the advanced ones like wOBA or linear weights. Sorry it is not a black and white number for you.