Who is the best defensive player in baseball? It sounds like a simple question. It may even have a simple answer… but considering the length of this article, probably not.

Traditional statistics say the best fielder in baseball last season was Todd Helton. His .998 fielding percentage was the highest in the sport. Helton handled the ball 1,035 times last season and made two errors, and that's quite good.

Verdict: Todd Helton!

There are a few problems with that.

Helton's fielding percentage measures how many errors he made, and errors are subjective. Sometimes a play qualifies as an error and other times a very similar play results in a hit. So Helton's error total is not the best way to determine the quality of his fielding. More importantly, fielding percentage only penalizes players for missing balls they actually get to. If Helton doesn't react quickly enough on a ground ball and it goes through for a hit, he isn't penalized, even though it was a play another first baseman might have made. Put another way, fielding percentage doesn't measure range: A player who reaches more balls but makes a few more errors is still turning more batted balls into outs than a player who reaches fewer balls.

Of course, there are even more problems with the idea of Helton as best fielder. Helton was 39 years old last season. A player that age could be solid, above-average even, but the best? Incredibly unlikely. Further, there's the eye test: Have you seen Todd Helton? He's in fine shape, but one wouldn't characterize him as fast, or agile, or limber, at least not when it comes to the realm of professional baseball players. (Compared to me, he's Mikhail Barishnykov.) So, no, the best fielder in baseball is probably not a now-retired 39-year-old first baseman with no speed and health issues.

Verdict: Not Todd Helton!

So who is it? To properly answer the question, we need to take a step back. What are the properties of a good fielder? Range, certainly -- so speed, but also ability to read the ball off the bat and react quickly. Good hands too, even though, as we've seen with Helton, without other attributes that won't cut it. A strong arm is helpful as well.

While all those are important, different positions have different defensive needs. A good catcher doesn't have to possess speed (though it doesn't hurt), but you can't be a good catcher without good hands. Good hands are also vital at third base, but they won't do you any good if you don't have an arm to get the ball to first base on a line. Center fielders don't necessarily require especially strong arms or even great hands, but speed is a prerequisite to play the position. So how do you compare a third baseman to a shortstop, or a catcher to a second baseman, or a center fielder to a first baseman?

This is about the right time to bring up the defensive spectrum. Bill James invented the concept, which he defined as "an arrangement of defensive positions according to raw abilities needed to learn to play each." In essence, it's a list of positions by difficulty. Just by watching baseball you've probably got a strong sense of this already -- for example, players sometimes are moved off shortstop, but rarely are players moved to shortstop. That's because shortstop requires the most athleticism, the strongest arm, the most range, and the most agility. Logically, we could say the best defensive player in baseball should be the player who best plays the toughest position to fill. So to answer the question, all you need to do is look up a list of shortstops, point to the name at the top, and there's your answer.

Verdict: A Shortstop!

But wait, what about catcher? If you look at James' defensive spectrum, you'll find catcher at the top, not shortstop, which means according to his list, catcher is the most difficult position to play in baseball. Add to that the new information about the value catchers provide that we've started to understand only recently and things get more complicated. Shortstops make a great number of defensive plays, the most of any position in the field, but catchers -- from calling a game, to dealing with the pitcher's psyche, and framing pitches and getting calls -- affect every single pitch of the game.

Verdict: A Shortstop Catcher!

If a catcher is the best defensive player in baseball, then that player just might be the incomparable Yadier Molina. (Getty Images)

Don't forget that players play behind different pitchers, with different fielders next to them, and in different ballparks (nobody would deny playing left field in Fenway Park is different than playing left field in Petco Park). How do you measure range, arm strength, speed, athleticism, and on and on, while comparing it across positions with different requirements, and adjusting it for different sized parks and in different leagues?

Verdict: AHHH!

A number of websites have attempted to tackle the quandary and have developed what they (and I) believe are better defensive statistics. Baseball Prospectus has FRAA (Fielding Runs Above Average). FanGraphs uses UZR (Ultimate Zone Rating) and DRS (Defensive Runs Saved). Baseball Reference uses Total Zone. FanGraphs and Baseball Reference both list other types of defensive stats as well. Click those links for more information, or be more direct about it and smash your face repeatedly into the side of the fridge. Alternatively, if self-destruction isn't your bag, read this excellent piece on the different defensive stats by Christopher Cwik.

Suffice it to say each stat, in essence, uses game data from once source or another and normalizes it to fit the context of the event. It can get very intricate and complicated, not least because each of the stats can give us different results. In 2012 the best defender according to FRAA was Aaron Hill, a second baseman. Total Zone had Michael Bourn first, and Ben Revere second, with Hill not in the top 10. Bourn didn't rank among the top 100 players according to FRAA. UZR had Bourn at the top and Jason Heyward second. Last season, the stats matched up a bit better. Manny Machado and Andrelton Simmons finished one-two in all three stats, but after that, results varied. This isn't really a criticism of the stats: They're all measuring slightly different things. There is no be-all-end-all defensive statistic that can definitively answer who the best defensive player is.

Verdict: The best defensive player is like the Sasquatch!

There is another issue I haven't even brought up yet, and that's sample size. Research tells us one season's worth of defensive data isn't enough to determine how good a player is. Sometimes a guy has a particularly good year, plays over his head, and other times a guy has a particularly tough year. Luck plays a role; teammates do too. Performance fluctuates, and thus the stats don't necessarily reflect a player's true talent. If you look at three years' worth of stats, that'll give you a reasonably accurate picture. The problem with that is three years worth of stats will tell you who the best fielder in baseball over the last three years was, or more accurately, who the best fielder in baseball over the past three years as measured by that particular stat was. But we want to know who the best defensive player is in baseball right now. There might be an overlap to those answers, but there might not be, and even if there is with one stat there isn't likely to be with all of them.

So what are we left with? We're left with better stats that can tell us far more accurately how a player has played, but that by itself isn't enough. There are two more things left to take into account -- and actually they're both sort of the same thing. First is scouting and analysis. That is, what do professional talent evaluators say about a player's defensive ability? If you follow a team you probably have a pretty good idea of what at least a few scouts say about a particular player's defense, but there is no centralized scouting database that collects and organizes opinions into searchable information, and different scouts will often have different opinions.

There's one more thing left to throw into the mix: our own opinions. Pay attention to what the stats say (each one of them), read what the scouts say, and watch the games. From those sources we can piece together what might be called an educated guess. It won't be definitive, but is certainly worth discussing and even arguing for.

So now that I've essentially said the best defensive player in baseball is up for debate, let me make an argument. Looking at all the data and listening to all the scouts and analysts, I think the best defensive player in baseball is Andrelton Simmons.

Verdict: Andrelton Simmons!

Yes, we're dealing with a small sample size, but the reason Simmons doesn't pass the three-year test is because he hasn't been in the league three years yet. Simmons is young, fast, agile, and oh, the highlights he generates. What's more, the stats love him. The new Baseball Prospectus 2014 calls him "Hands down the best defensive shortstop in baseball." 

Thing is, I think you could make a strong argument for a catcher, perhaps Matt Wieters or Yadier Molina. The value catchers generate through pitch framing and game calling is still something we're learning about, and as such I'm reluctant to wholly subscribe to the numbers. But if you did, you might see Wieters on top of a few defensive lists, like this one.

Verdict: Matt Wieters!

That said, I think the difference between the best and worst shortstop is greater than the difference between the best and worst catcher. 

Verdict: Andrelton Simmons!

Manny Machado has a case as well....

Verdict: Manny Machado!

…although Simmons plays a tougher position and does it better than Machado.

Verdict: Andrelton Simmons!