On Wednesday night, the Braves shut down the Padres behind another strong start by deadline trade target Paul Maholm. Thanks to a 27-13 run since the start of July, Atlanta’s record stands a season-high 18 games over .500. However, while the Braves have nipped at the first-place Nationals’ heels—at times this month, only two games have separated the NL East’s top teams—they haven’t been able to close the gap completely. The Nats, who won their own game Wednesday on the strength of six precious innings from Stephen Strasburg’s dwindling supply, have matched them win for win.

However, while the Nationals own the NL’s best record, they haven’t yet locked up a division title. Washington won’t have Strasburg on its side for much longer, and the Braves will be right behind them, waiting to capitalize on any sign of weakness. Both teams boast playoff odds north of 90 percent, so neither is likely to miss the postseason (though after the way things went for the Braves last September, they probably aren’t taking a trip to October for granted). But the real prize—a first-place finish, and a guaranteed ticket to the first round of the playoffs—remains at stake. The Nats have the better pitching staff and defense, and both teams are evenly matched on offense. But the Braves do have a sizeable advantage over the Nats in one often-overlooked area: baserunning.

How a team hits, pitches, and fields has more to do with its place in the standings than its performance on the basepaths. However, if two clubs are close to evenly matched in most respects but differ greatly in their ability to take the extra base, that difference can prove decisive. Baseball Prospectus offers a stat called Baserunning Runs (BRR), which measures the number of runs a player adds or subtracts by advancing more or fewer bases than expected, given his number of opportunities. The Braves and Nationals couldn’t be any farther apart on the team BRR leaderboard: Atlanta is baseball’s best baserunning team, with 13.7 BRR, while Washington is the worst, with -14.9. The Braves have been almost four runs better than the next-best baserunning team, while the Nats fall a full five runs below the next-worst.

By no means is an inability to run the bases a fatal flaw for Washington. The 2011 Cardinals, last year’s World Series winners, also posted the lowest BRR in the big leagues, though the Cardinals’ BRR wasn’t quite as bad; not since the 2009 Orioles has a team finished a season with a BRR as low as the Nats’, and not since the Curse-killing 2004 Red Sox has a team run as poorly and still made the playoffs. Washington can overcome its weakness, but the team’s bad baserunning is still a significant obstacle in the way of an easy victory over Atlanta. The difference due to baserunning between the two teams amounts to nearly three wins, which means that the Nationals’ lead would nearly be doubled if the clubs’ rankings were reversed. And if the Braves do manage to make a run and beat out the Nats by a game or two, they’ll have their ability on the basepaths to thank.

We can dig a little deeper to see exactly where the Braves are excelling and the Nats are falling flat. The Braves owe their baserunning prowess almost entirely to Michael Bourn and Jason Heyward, who rank first and third in the majors, respectively, in individual BRR. Bourn and Heyward have combined for 15.4 runs on the bases, which means that their teammates have been a net negative. However, Atlanta lacks any truly terrible runners—fragile 40-year-old Chipper Jones brings up the rear at -2.6—and the two speedsters have been a dangerous enough duo to lift the rest of the roster. Thanks largely to them, Braves baserunners have scored in 33 percent of their times on base, tied for the highest percentage in baseball. (Major-league average is an even 30 percent.)

The Nats lack any individual performances as extreme as the Braves’, ranging from Adam LaRoche (-3.7) at the low end to Ian Desmond (4.2) at the high end. However, the distribution is tilted toward the negatives: the Nats have only two players who’ve contributed more than one run with their legs (Desmond and Bryce Harper), but 11 who’ve given at least one away (including Strasburg, who might not be good at everything after all). Washington’s bad baserunning has been a true team effort.

The Nationals’ primarily problem isn’t necessarily speed. In fact, the Nats have the third-youngest collection of position players in the majors, with an average age of 27.1, so we wouldn’t expect them to be especially slow of foot. Fortunately, BRR is broken into five components, each of which captures a team’s or player’s aptitude at a particular aspect of baserunning. This enables us to isolate the ones in which Washington struggles most.

The Nationals place in the middle of the pack in Stolen Base Runs, which makes sense, given that they also rank roughly in the middle of major-league teams in total steals and attempted steal success rate. They struggle the most when attempting to advance on hits, namely from first on singles, from second on singles, and from first on doubles. That failure to make pitchers pay as much as possible for surrendering hits can be blamed for -11.7 of their -14.9 total. Nationals baserunners have taken more than one base on singles and more than two bases on doubles only 38 percent of the time, compared to the 41 percent major-league average.

Players tend to get worse at advancing on hits as their ages climb and wheels decline, but perhaps the Nats are still so raw that they haven’t yet learned to anticipate where batted balls will land, get good jumps, and avoid being fooled by outfielders. If that’s the case, experience and coaching and could solve some of their problems, though there probably aren’t any latent Bourns or Heywards lurking on the roster. The Nats have found success this season by allowing fewer runs than any other team, not by scoring more. But when it comes to baserunning, it wouldn’t hurt them to be a bit more like the Braves.

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

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I may be biased (as an unabashed Braves fan), but I do feel that the Braves defense is every bit as good as that of the Nats if not better, especially once Simmons comes back from his thumb injury. The Braves outfield defense is historically great, and while Uggla is generally a black-hole, Chipper and Freeman have been league average given their age and range-issues, respectively, and Simmons is probably the best SS in the game defensively, small sample aside.
As a Nationals fan, I point you to the following helpful statistic regarding team defense:

Note that WAS is 2nd (as of this writing), ATL 16th.
I agree. According to UZR the Braves have the 2nd best defense in MLB. According to UZR/150 the Braves have the best defense in MLB. The Nats are ranked about 10th in MLB using those stats.
What we know for sure is that the Braves give up an essentially league average number of hits on balls in play. What UZR asserts is that the Braves' defense is so gifted that it's masking an especially difficult distribution of balls in play, that for a team with a less gifted defense would result in a substantially worse than average hits allowed rate. Now, is it possible that this is true? Yes. I don't think it's especially likely, though, and I have many reservations about the ability of UZR to measure that sort of thing accurately.
Perhaps if the Nats' pitchers stopped getting on base, they could improve their team baserunning stats.