Just keep in mind that watching someone play can be misleading too. If all you could do in baseball was watch, you'd likely not be able to accurately rank the hitters on your team from best to worst. You might not notice that Smyly has an unusually good level of success against righties when there are runners on base, etc. In the D Rating stat, one way to get confidence in it is to look at who ranks highest and lowest on each team and see if it jives with your perception. Once you realize that it does, then you can use it as a tool to question the odd results or to gain insight into players on teams that you don't have a long history of eye witness scouting on. On the Knicks, this stat ranks Sheed, then Kidd, then Kurt Thomas as the top 3 defenders and Anthony and Novak toward the end. On the Celtics, it has KG, then Pierce, then Rondo. On the Lakers, it is Howard, then Kobe and Meta with Nash toward the bottom. This is a per 100 stat, so it has nothing to do with playing time and it is defensive, so there is no usage bias. In general though, big men rank higher on the rankings because they are big and they affect the game positively on the defensive end of the court. Usually, smaller players are added to the mix for offensive purposes and there is an optimization. Imagine a league where you have 5 guys on each end of the court and they could remain there. What would your ideal defensive team look like? In summary, a big man can seem weak defensively but still be one of the most effective defenders on the team. Just to give a further example, Monroe might be in the right place at the right time defensively more often than another player, but Monroe may not be as effective once he's in that position to stop the shot. He might be better defensively overall, but there might be more times than the other guy where somebody scores right over him and he looks unathletic. I don't think Monroe looks great on D when I watch him play either, except for steals, positioning, strength/ holding post position on D, and defensive rounding. But those are important things that maybe add up. If I saw that he ranked in the middle of the pack on DRAT, I'd conclude that he was giving it all away and more with his inability to block shots. But since he ranks at the top, I'm thinking that he probably does a lot of fundamental things well that we don't fully appreciate yet. In 2012, Monroe was right behind Ben Wallace in DRAT on the team, so this is 2 consecutive years that he rose the top of this stat.