With a 7-6 win over the Diamondbacks on Wednesday night, the Pirates ran their record to 63-47, pulling within 2 ½ games of Cincinnati in the NL Central. They remain tied with Atlanta atop the NL Wild Card standings. If the season ended today, the Pirates would be a playoff team. That’s not something we’ve been able to say very often after April in the last 20 years.

Last year at this time, the Pirates were in mid-free fall, fresh off a 10-game losing streak that put them under .500 for good. This year, that collapse isn’t coming. Pittsburgh’s 2011 team had a -39 run differential on this date last season, but this year’s edition has outscored its opponents by 35 runs. The Pirates haven’t played as well as their record would indicate, which explains why their playoff odds still sit below 60 percent. But even if their two-decade postseason appearance drought does go on a little longer, their streak of consecutive sub-.500 seasons is about to end.

Scoring hasn’t been Pittsburgh’s strength. Although the Pirates have hit better this season than they did last year, when they finished with a major-league-low .244 True Average, they’re still a below-average offensive team. However, the club has taken bigger strides on the other side of the ball. Pittsburgh’s pitching has gotten most of the credit for the team’s improved run prevention, but some of that credit should go to the team’s tighter defense, the secret ingredient behind the Pirates’ surprising success.

In 2010, the Pirates finished dead last in the majors in defensive efficiency, a measure of the rate at which balls in play are converted into outs by a team’s defense. Last year, they improved only slightly, raising their ranking to 25th. This season, the Pirates’ defensive efficiency is tied for second-best in baseball. The team’s fielders have converted 72.2 percent of balls in play into outs, compared to 68.9 percent in 2010. That might not sound like much of a leap, but with between 4,000 and 5,000 balls in play allowed per pitching team per year, a gain of only a few percentage points means hundreds of extra outs recorded. Those extra outs both lighten the load on the pitching staff and decrease the damage done against it. It’s not a coincidence that the Pirates’ last winning season, 1992, was also the last in which the team finished in the top 10 in defensive efficiency.

When people think about dramatic team turnarounds on defense, the 2008 Rays are often the first team to come to mind. The Rays went from being one of the worst defensive teams of all time in 2007 to the best in baseball in 2008, making the playoffs for the first time as a franchise after 10 sad-sack years in the AL East cellar. Although the Rays traded for skilled defensive shortstop Jason Bartlett and good-gloved outfielder Gabe Gross before that season, they achieved most of their upgrades by rearranging assets already under team control, promoting Evan Longoria from Triple-A Durham, shifting Akinori Iwamura from third base to second, and moving B.J. Upton to the outfield full time.

The Rays’ fielding quick fix was the most successful year-to-year defensive overhaul in history. The Pirates’ makeover has been a little less extreme. Like the ’08 Rays, the Pirates imported a shortstop known more for his glove than his bat in Clint Barmes. Barmes has hit poorly even by his standards, but he’s delivered on defense. The team also rid itself of Ryan Doumit, whom BP’s Max Marchi rated as the second-worst defensive catcher over the period from 2008-2011. Although Doumit has been productive at the plate for the Twins this season, his defensive struggles made him a poor fit for an NL team. Offseason signee Rod Barajas is a much better backstop.

The Pirates have also seen improved performances from their returning players. Alex Presley has played more than he did as a rookie, which has helped optimize the outfield defense. Second baseman Neil Walker is having his best season yet at the plate, but he’s also boasting a much-improved FRAA for the second straight season. Walker began his professional career as a catcher and later moved to third before learning second on the job at the major-league level in 2010. Another season at second—and another spring training working with legendary defender Bill Mazeroski—seems to have made his glove more dependable. Pedro Alvarez has made similar strides at third. The Pirates deserve credit for resisting the urge to move both Walker and Alvarez to less demanding defensive positions despite some evaluators’ doubts that they were up to the task. It’s also worth mentioning that the Pirates are one of the few major-league teams that still take pre-game infield practice on a regular basis. Practice alone didn’t turn the Pirates into a good fielding team, but it may have helped them maximize their defensive potential once they put the right personnel in place.

The Pirates have made the biggest gain in defensive efficiency since last season, but they aren’t the only contending team to benefit from more sure-handed fielders. Two surprising first-place teams, the White Sox and the Nationals, have also upped their efficiency in the field. The Nationals have been the best fielding franchise in baseball this year after finishing 12th last season, and the White Sox have improved by almost as large a margin as Pittsburgh, rising from 29th last year to eighth in 2012. Meanwhile, the preseason consensus favorites in the AL Central, the Tigers, have thus far failed to pull away, partially because they’ve fallen from the middle of the pack to 27th in defensive efficiency (one defensive development that took no one by surprise).

The White Sox have made their most meaningful improvements by moving Alex Rios from center to right, where FRAA credits him with over 11 more runs saved in the field relative to his positional peers than it did last year, and installing Alejandro De Aza and Dayan Viciedo as their other full-time outfielders. Orlando Hudson has given them good glove work in the infield, though like Barmes, he hasn’t hit. The Nats’ more modest improvements have come primarily from the promotion of Bryce Harper and returns to health for Adam LaRoche and Ryan Zimmerman. In the Pirates’ and Nationals’ cases, it’s possible that improvements to the pitching staffs, independent of the defensive upgrades, have led to some weaker contact that has merely made fielders look more efficient. But that can’t explain all of the improvement. Better gloves have been responsible for a portion of these clubs’ newfound ability to prevent runs.

Defense is still one of the most difficult aspects of performance to project, and the acquisition of an established arm or a big bat is still more likely to make headlines than a signing, position switch, or promotion intended to improve a team in the field. Maybe that’s why we didn’t see the success of the Pirates, White Sox, and Nationals coming. And maybe looking a little more closely at the leather is one way we can make next year’s surprise teams a little less surprising.

​A version of this story originally appeared on ESPN Insider Insider.