Is this the best Cubs defense of all time?

— -- CHICAGO -- The Chicago Cubs have the best defense in baseball. It might be the best team defense we've seen in some time -- quite some time.

Historically, so much of defensive evaluation has been anecdotal and, therefore, inconclusive. Even now, with rivers of data flowing into our collective hardball consciousness, we haven't reached the point where we can make specific judgments about defense with any real certainty. Still, I am more or less certain that the Cubs are playing unusually special defense.

"Just through a natural progression, maturity-wise, some guys have just gotten better," Cubs manager Joe Maddon said. "Because they're good. We're making the routine play routinely. We've made some pretty spectacular plays all over the field."

The crazy thing though is that the Cubs seem aware that they're good on defense, you don't get the sense that they understand just how good they are.

"I never look at the numbers on defense," said outfielder Jason Heyward, who, by the numbers, has been the second-best fielder in all of baseball. "We just have a lot of guys who do things the right way."

When putting this piece together, I came up with a metric that was so surprising -- to me -- that I've decided to save it for the end of the story -- like a 1950s serial. We'll build up to that end. Let's start by burrowing into the ESPN database to present the leaderboard for single-season, team defensive runs saved the past five years. Numbers for the 2016 season have been prorated to reflect 162 games.

Through Wednesday's games, the Cubs' 62 defensive runs saved are 11 more than the second-place Astros' total and lead the majors. With a strong finish, the Cubs could threaten the 2013 Royals for the best total in this category in the past half-decade. Those Royals won the past two AL pennants with killer defense that ran laps around the rest of the big leagues. From 2013 to 2015, Kansas City amassed 205 runs saved -- 44 more than second-place Arizona and 83 more than third-place Pittsburgh. But this season, the mantle of best-in-the-game defense has shifted from Kauffman Stadium to Wrigley Field.

"Last year, [defense] was definitely an important part of that club," said jack-of-all-gloves Ben Zobrist, who won a ring with last year's Royals. "I think the outfield, they planned on their pitchers who were more fly ball pitchers. Hitting the ball around the ballpark and then going and catching it. This year, [ Dexter Fowler] I know has taken a deeper approach in this outfield than [the Cubs] did last year. Numbers-wise, it's made a huge difference."

We still can't tease out exactly how much of run prevention in baseball is pitching and how much is fielding. But we do know the Cubs have a pretty good pitching staff -- perhaps the best in the majors from top to bottom, rotation to bullpen. Their 3.13 team ERA leads the big leagues. However, Chicago's 3.76 fielding-independent pitching ERA (FIP) ranks "only" fifth.

This suggests two possibilities. Either the pitching staff is allowing the kinds of balls-in-play that favor strong defensive efficiency or the defense is giving the staff a boost. Likely, it's a combination of both.

Cubs pitchers have allowed line drives on 20.4 percent of their balls in play, an unremarkable number. It's lower than the big-league average (20.9 percent) and ranks 12th in the majors. However, the Cubs also have the lowest "well-hit" average in the majors (.123), a metric that estimates just what it sounds like: How many of the opponents' balls in play have been well struck?

The pitchers clearly play a key part in this story. Nevertheless, at the bottom line, the Cubs have the biggest gap in the majors between actual ERA and FIP:

"We're almost spoiled," Cubs pitcher Jason Hammel said. "The guys go out there and play nine hard innings for us, and they take hits away. As long as we're in the zone, throwing strikes, putting the ball in play, the guys are going to make the plays."

Because I mentioned balls in play, let me drop my first pretty amazing stat: The Cubs lead the majors with a .257 average on opponents' balls in play. Second place? That would be the Dodgers at .280. The big-league average is .299.

But that isn't my pretty amazing stat. According to baseball-reference.com, that .257 mark is the lowest in Cubs' history since 1920, surpassing the .262 BABIP allowed by the 1952 and 1955 Cubs. Some league context is ignored in that measurement, but for now, let's accept it for what it is. Regardless of era, this year's Cubs are turning more balls in play into outs than any other Cubs team did during the live-ball era.

"If the metrics really like us, that's great," Maddon said. "From an old-school perspective, mechanically, I really like the way we're moving. The feet have gotten better. The arm strokes have gotten shorter."

The Cubs don't have any holes in their defense, and they have more good defenders than they can get on the field. They rank 15th or better in runs saved at every position. They have five individual defenders in the top five at their positions: Anthony Rizzo at first base, Javier Baez at second, Addison Russell at shortstop, David Ross at catcher and Heyward in right field.

The only sore spot on the defensive dossier is the trouble catcher Miguel Montero has had throwing out opposing base-stealers (three of 52 attempts), but even he ranks high in some aspect of defense, as he is sixth in runs saved with his pitch-framing. Meanwhile, Ross and Contreras both excel at limiting the running game.

The Cubs have two players who lead the team in runs saved at two positions: Heyward (right and center field) and Kris Bryant (third base and left field). Heyward ranks second in all of baseball in total runs saved. Shortstop Russell is 16th. Baez is 33rd, even though he has played multiple positions and has been on the field only about two-thirds of the time overall.

"The fact we have so many guys who play various positions well, that's got to start happening in other places, other organizations," Maddon said. "It's so beneficial game-in-progress. We're able to do all these different things because of athleticism and adaptability. Javy really sets that up. We have these interchangeable parts that I think maybe bleed into this defense metric."

We have barely mentioned Zobrist, long one of the most versatile and steady defenders in the game. He currently ranks second in the majors in fielding percentage at second base when he isn't playing in the outfield. Up and down the roster, the Cubs have walking arguments for baseball adopting a multi-position Gold Glove award.

"I'd love that, the super-[utility], all that. I think that should be a position on the All-Star team," Maddon said. "We should also actually vote it as that guy. I've thought since 2009 with Zobrist."

We can't forget that one mad scientist, Maddon, who moves all the pieces around like a chess master. Nor can we forget the coaching staff that sets up the daily defensive game plan. If something plays to the percentages, Maddon will do it. But he doesn't feel compelled. Shifting is more prevalent than ever before in baseball, but the Cubs don't shift very often by current standards. That said, when they shift, they shift very well, as they are allowing the lowest opponents' average on shifts, just .251, nosing out the Dodgers' .252.

"We don't shift that often, but I think that's more of a product of the league and the teams we play against," Maddon said. "It's not that we don't want to."

This all paints a pretty picture, and the brushstrokes are mostly complete. I've thrown a lot of superlative numbers at you, but I haven't gotten to the one I was most excited about. We'll finish with that.

This metric is related to the amazing BABIP figure I tossed out before: Chicago's .257 opponent BABIP is leaps and bounds above that of everybody else in baseball. The inverse of BABIP is defensive efficiency record (DER), or the percentage of balls in play that a defense turns into outs. Simply taking 1-minus-BABIP gives you a good approximation of DER. By this method, the Cubs' DER this season is a best-in-baseball .743.

DER is a metric that is sensitive to league context. According to baseball-reference.com, the National League DER in 1930 was .687. In 1942, it was .734. If we're going to compare teams across eras, we need to adjust for this. I did so using a straightforward method: I looked at the DER of each team since 1920 in a ratio with its league average.

Then I got very excited in the way only the truly geeky can get:

*microphone drops*

"We all make efforts to do something on that side of the ball," Heyward said. "We understand that that can win you games."