Advanced metrics don’t tell the whole story about the Royals’ spectacular defense. After all, there are the diving catches, the leaping grabs and the all-out dead sprints to the wall that narrate Kansas City’s defensive tale just fine.

But advanced metrics can tell part of the story, including why the defense could be even better this season.

According to Baseball-Reference.com’s dWAR, which measures how many wins above replacement a player is worth on defense, the Royals put together one of the best defensive seasons in baseball history. They were the first team ever to have two outfielders with dWARs greater than 2.5 — Lorenzo Cain at 2.7 and Alex Gordon at 2.6.

They were the first team since the 1973 Orioles with four players with a dWAR at or above 1.9 — catcher Salvador Perez checked in at 2.1, while outfielder Jarrod Dyson was at 1.9. Each of Baltimore’s quartet — Brooks Robinson, Bobby Grich, Paul Blair and Mark Belanger — won a Gold Glove that season and combined for 36 career Gold Gloves.

So how do the Royals improve on one of the best defensive seasons in history? Well, by first being the best defense in a season.

Last year, shockingly, Kansas City didn’t boast baseball’s best defense, at least according to dWAR. That honor went to Baltimore, which posted a cumulative 7.2 dWAR, but had only one player above 2.0 (J.J. Hardy at 2.1). Kansas City’s 5.8 total dWAR was second.

The Royals had plenty of pluses on defense, but also had their share of minuses. But entering this season, the biggest minuses are no longer on the roster. The five Royals who had the worst dWAR in 2014 — first baseman/DH Billy Butler, right fielder Nori Aoki, outfielder Justin Maxwell, outfielder Raul Ibanez and infielder Danny Valencia — are all with other teams this season.

The five players combined for a minus 4.7 dWAR, although they could have been victimized by a small sample size. The only regular defensive player was Aoki (120 games in the outfield) while the other four combined for 96 games in the field.

The Royals added Alex Rios to replace Aoki in right field and Kendrys Morales to take over Butler’s role — everyday designated hitter, occasional first baseman — although neither is known for his glove. Rios and Morales combined for a minus 1.7 dWAR, which is still about a win better than the Aoki-Butler pairing.

The new guys are an upgrade defensively, but the old guys can still improve on their 2014 numbers.

Two-time Gold Glove winner Eric Hosmer’s defense has improved each season in the majors (although he still sports a career minus-4.0 dWAR). Perez, also a two-time Gold Glove winner, threw out 30 percent of would-be basestealers and led the majors with 44 runner kills, the total number of baserunners thrown out. He’s only 24.

Gordon, a Gold Glove winner in each of the last four seasons, became the second outfielder 30 or older with a 2.5 dWAR season. Tony Gwynn first did it in 1991 at age 31. Cain, who has never been a Gold Glover, had the second-highest dWAR in the American League last season despite playing 28 fewer games than leader Ian Kinsler.

The new additions, combined with continued improvement from Kansas City’s young stars and established stalwarts, could make the Royals’ defense historically great — again.

Now, they just have to be the best one in 2015.

You can follow Matthew DeFranks on Twitter at @MDeFranks or email him at matthew.defranks@gmail.com.