Is Curtis Granderson a good center fielder? If you consult defensive metrics, it depends on the year. From 2006 to 2007, Granderson was considered one of the game’s best. He ranked second among center fielders in UZR with 27.5 runs saved above average. Only Andruw Jones, in his final days as a good player with Atlanta, was better. In 2010, Granderson was still pretty good. He saved 6.4 runs above average with his glove, according to UZR, good for fifth in the majors among center fielders. He was 0.2 runs below Franklin Gutierrez, then acknowledged as a defensive wizard with Seattle. Then again, look at 2008. Granderson cost Detroit 11.1 runs in the fielding, UZR said. The statistic said even worse things about Granderson in 2012. Granderson was the worst center fielder in baseball, worth -17.8 runs. That, we suppose, is not good. So what happened? Did Granderson suddenly forget how to field his position in 2008 and 2012? Why was he so excellent in other years? UZR isn’t the only fielding metric, but it’s likely the one with the widest acceptance. It’s also something of a work in progress. Year after year, we see the numbers fluctuate. Take Andrew McCutchen. He was terrible in 2010 (-13.7 runs). He was good in 2011 (+3.5). He was bad again in 2012 (-6.9). Or Josh Hamilton. Terrible in 2008 (-14.6). Great in 2010 (+9.8). Terrible again in 2012 (-12.6). Maybe defensive skills really do vary in such wide swings from year to year. But it’s really hard to tell. The metrics are still being improved upon each season. They will get better. But they don’t tell the whole story, not just yet.