Denard Span has been on a tear in the second half. Is he the reason for the Nats' success?

Throughout much of the first half of the season, the Washington Nationals were in a seesaw battle with the Atlanta Braves for the lead of the National League East division. The Nats were a middle-of-the-pack team in terms of runs scored (15th overall) and struggled to put any distance between themselves and the Braves, never going more than two games up (although never falling more than four games back either).

Currently, the Nationals have an 11.5 game lead over the Braves and, with a win tonight, will clinch the division title. What happened in the second half to lead to such a swing?

Slowed By Injury?

The easy narrative is to say that the Nats were slowed by injuries in the first half of the season, and once they got some key players back (Bryce Harper, Adam LaRoche, Wilson Ramos and Ryan Zimmerman), the offense picked up and they started scoring more runs.

While getting healthy certainly didnâ€™t hurt their second-half success, equally important was Denard Spanâ€™s starting to hit for a high average and getting on base at a high rate. Letâ€™s check out his first and second half splits, first using â€œstandardâ€ stats, with the number in parenthesis being his MLB rank. (All numbers via FanGraphs).

Season BA OBP SLG OPS Hits Runs SB 1st Half .269 (84) .319 (106) .385 (109) .705 (111) 61 (154) 57 (22) 15 (T-17) 2nd Half .381 (20) .403 (7) .459 (41) .862 (22) 79 (T-1) 36 (9) 16 (4)

During the first half of the season, Span struggled to do anything besides score runs and steal bases. Teams can live with their leadoff hitters batting around .270, but when their on-base percentage (OBP) dips to just above league average (which is currently .314), then there is a problem.

The leadoff hitter has the potential to be the team catalyst, so when this key hitter doesnâ€™t get on base, scoring runs can be difficult. Like they say, itâ€™s hard to score runs if no one is on base. Span has been on base a lot in the second half â€“ his OBP ranks seventh best in baseball â€“ which is helped by being tied for the most hits in the second half as well. The Nationals went from 15th in runs scored as a team in the first half to scoring the fourth most in baseball in the second half and can thank Span for it.

Now letâ€™s look at some of his â€œadvancedâ€ stats to see if they tell the same story.

Season fWAR wOBA wRC wRC+ wRAA BsR 1st Half 1.5 (88) .312 (110) 41.8 (96) 97 (112) 0.4 (110) 3.2 (16) 2nd Half 2.4 (5) .381 (20) 41 (8) 144 (T-19) 13.81 (13) 1.9 (T-16)

Again, Spanâ€™s base running is the only constant, as his base running runs above average (BsR) ranking is the same in both halves of the season. His rankings everywhere else are vastly improved, with his wins above replacement (fWAR) being the fifth best in all of baseball during the second half, better than even Mike Troutâ€™s 2.1.

Spanâ€™s weighted on-base average (wOBA) is his lowest rank on this table at 20th, but is impressive nonetheless, with the likes of Giancarlo Stanton, Jose Abreu, and Jose Bautista ahead of him (but again, not Mike Trout).

His weighted runs created (wRC), which according to FanGraphs quantifies "a playerâ€™s total offensive value and measure it by runs,â€ is good for eighth best during the second half. This stat is great for evaluating a hitter because it, â€œcredits a player for total production rather than on an at bat by at bat basis,â€ unlike, for example, batting average does. Spanâ€™s advanced stats are consistent with his standard ones and show how much of a tear heâ€™s been on in the second half, helping the Nationals take a commanding lead of the division.

Thereâ€™s no denying Spanâ€™s amazing second half, but he has had some help scoring runs. Anthony Rendon (and his seventh best fWAR of 5.8) hits directly behind Span, followed by Jayson Werth and his .368 wOBA, which is good for 21st best in baseball. Adam LaRoche hits after Werth and his 24 home runs are tied for the 20th most in baseball, so Span isnâ€™t the only player on his team having a good season. With that said, he is the teamâ€™s table-setter, and in the second half has given his teammates plenty of opportunities to drive him in and, more importantly, help the Nationals win games.

The Nats posted a record of 51-42 in the first half, which is a winning percentage of .548. In the second half, their current record is 35-21, a winning percentage of .625. And they show no signs of slowing down.

If Span continues to get on base at his current high rate, this is going to be a tough team to beat in the playoffs, as any of the players hitting after him are capable of driving him in. A lineup that has Bryce Harper hitting sixth is one without any holes, and one that Span has been making thrive. If we combine his ability to get on base with his savvy base running and speed on the bases, we realize that the Nats have the perfect leadoff hitter playing his best as they are about to enter the playoffs.