A team that has dramatically improved it's defense is more likely to findpitching breakouts than the other way around. For those of you unfamiliar with UZR I've borrowed a description from Baseball Think Factory (this link is a good one to read) :
UZR rate is expressed as a fraction of 1, the same as a simple ZR (ZR). A UZR rate means essentially the same thing as a simple ZR � namely the number of balls fielded (turned into at least one out) divided by the number of chances; however, UZR rate is a weighted average of a player�s ZR in each of several zones.
As you will see, UZR rate is really a by-product of UZR runs, and UZR runs is the heart of the UZR system. It represents the value of a fielder�s performance expressed as runs saved or cost, in comparison to an average fielder (actually in comparison to the mean performance of all fielders) at that position, in that player�s league, and during that particular year. UZR runs is the defensive counterpart of Palmer�s offensive linear weights (lwts); thus it can be combined with lwts (among other things) to give you an estimate of a player�s total offensive and defensive value. Any player with an average defensive performance will, by definition, have exactly zero UZR runs.