Rays season in review 2015: Daniel Nava

Before being claimed by the Rays on August 5, Daniel Nava had spent all of his major league career with Red Sox, and was beloved by much of their fan base.

With Boston he was almost exclusively a platoon player, despite being a switch hitter, with the majority of his plate appearances coming against right handed pitchers and he initially thrived in this role, posting a .385 OBP and a 127 wRC+ in his first full season in 2013. But after he got off to a slow start in 2014, Nava was sent down to Triple-A Pawtucket at the end of April. The reset worked, and upon his promotion in June of 2014, he posted a 115 wRC+ in the second half.

The start of the 2015 season nearly mirrored that of the 2014 season. Nava again got off to a slow start, this time with a .152 batting average and wRC+ of 1 and 51 in April and May respectively. Nava cited inconsistent playing time as a cause of his struggles at the plate, saying, "It's definitely more of a challenge to break out of slumps and find your rhythm when you're not playing every day."

With many options in the outfield for the Red Sox, Nava's margin of error was small. After being sidelined with a left thumb strain for nearly two months, the Red Sox couldn't afford to wait any longer and Nava was designated for assignment shortly after he returned.

He became the only successful waiver claim by the Rays after 2015's trade deadline, and with a new lease on life Nava looked like he was beginning to turn his season around. The following table shows the dramatic difference between Nava's performance with the Red Sox and Rays in 2015.

2015	AVG	OBP	SLG	wRC+	WAR
Red Sox	.152	.260	.182	24	-0.4
Rays	.233	.364	.301	99	+0.2

In addition to Nava's slash line improving, his wRC+ jumped from being terrible to league average. This indicated that not only were his traditional surface stats improving, he was being much more productive as a whole.

Despite these improvements, Nava wasn't close to as productive as he had been in the past. Let's look at some potential causes for Nava's rebound with the Rays, and whether or not these changes are likely to continue into next season.

It is important to note, however, that we are dealing with small sample sizes, as Nava recored 78 and 88 plate appearances with the Red Sox and Rays, respectively, last season. The statistics haven't reached a level where they will "reliable", and we shouldn't put too much stock into performance from each sample, but by looking at trends rather than being overly specific with values, we can try understand the dichotomy that was Nava's 2015 season.

Changes in Batted Ball Rates and Distributions

Which version of Daniel Nava is real? The heroic 2013, the inconsistent 2014, or the average 2015? Looking at batted ball rates, there is a clear change in Nava's distribution between his time with the Rays and Red Sox in 2015.

The most prominent increase comes from his line drive rate.

Before the 2015 season, Nava's career line drive rate was 22.5%, which is slightly above league the league average of 20.9%, but not so extreme that it seems unsustainable. However, with his time with the Red Sox in 2015, his line drive rate cratered, falling to 14.0%.

Had Nava sustained this rate for the whole season, it would have been second lowest in the league among qualified hitters. Once he joined the Rays, his line drive rate jumped to 22.2% which falls back in line with his career rate.

In addition to a low line drive rate, Nava's spray charts with the Red Sox in 2015 showed a pull tendency that he hadn't shown in any of his full seasons before this.

The image above shows an increased pull tendency with the Red Sox in 2015 that Nava didn't have in his first three seasons or with the Rays in 2015. In pulling the ball more, Nava hit fewer balls to the opposite field and up the middle.

Farrell suggested at the end of April that Nava was getting unlucky, saying, "He's squared some balls up but he's hit into some shifts... You don't see any glaring flaws in the swing path or the approach." He wouldn't have the time to battle those dragons, though Nava landed on the disabled list with a sprained thumb at the end of May, which effectively ended his career with the Red Sox and led him to Tampa Bay.

Resulting Drop in BABIP

From a theoretical view, it is easy to see how these changes in batted ball rates and distributions hurt Nava's performance.

Line drive have the highest BABIP of all batted ball types, at .678. Hitting fewer line drives and more ground balls (which have a BABIP of .236) effectively cost Nava hits, as ground balls result in hits at a much lower rate than line drives.

A lower line drive rate and oppo% contributed to Nava's sharp drop in BABIP, from .336 in 2014 to .200 with the Red Sox in 2015, as both components are positively correlated with BABIP. We can confirm that using an xBABIP formula which utilizes both of these stats, like the one created by Alex Chamberlain at RotoGraphs.

	xBABIP	BABIP
Red Sox 2014	.312	.336
Red Sox 2015	.264	.200
Rays 2015	.332	.302

These problems appeared to be resolved with the Rays. The previous graph of batted ball rates shows that Nava's line drive rate in Tampa Bay surpassed his previous career rate, and his oppo% rebounded with the Rays as well.

Nava's change in line drive rate may look like it suggests a change in performance or approach, but Bill Petti's work with year to year consistency of batting stats suggests otherwise. In his study, he showed that line drives had a year to year consistency of only .22, meaning that line drive rates fluctuate greatly between seasons.

Nava's small sample size amplifies the effect any small or potentially random fluctuations might have, though, so it can be challenging to tell if the increase in line drives comes from positive regression or random variation.

Nava in 2016

Nava's surface stats reflected the line drive rate and oppo% rebound with the Rays. His wOBA improved from .214 to .310, and his OBP moved from .260 to .364. But what sort of performance can we expect going forward?

While it's hard to pinpoint an exact projection, I believe we will be closer to Nava's performance with the Rays in 2015.

It's not simple enough to say that Nava appeared to be unlucky in his short time with the Red Sox in 2015. It was the crowded outfield situation that likely forced the Red Sox' hand to let a talented player go, but even though he made a partial rebound with the Rays, we can't completely disregard the first half of the season.

So while I believe that his true performance is closer to that with the Rays than with the Red Sox in 2015, we can't expect "127 wRC+ Daniel Nava" to make a return either.

The bigger issue is whether Nava is going to be worth the spot on the team next year.

Nava's utility is limited, as he is essentially only used against right handed pitchers despite his switch-hitting ability, and he is projected to make $1.9 million next year in arbitration, according to MLB Trade Rumor's early projections. Still, Nava has shown to be effective in the past when used appropriately - he recorded a 119 wRC+ against righties over his career - and has the added defensive benefit of being able to share time at first base.

Additionally, the Rays need a left handed bat on the roster. Without delving too far into the Rays potential offseason approach, many decisions will hinge on whether the Rays pay James Loney the $8 million he's slated to make or trade him to free up some money. Kevin Kiermaier is the only left handed hitter who looks to be guarantee for the roster next year, as Grady Sizemore, John Jaso, and Asdrubal Cabrera each have the chance to be elsewhere in 2016.

The need for depth from the left side is clear, and combining Nava's history of success with his low salary and positional flexibility, the Rays should hold on to the out-of-options outfielder, particularly when considering the open market.

Last season was certainly ugly at some points, but the free agent crop of left handed hitting outfielders doesn't look too appealing. Players like Jason Hayward will likely land out of the Rays price range, and other options look worse than Nava (like Matt Joyce, Ichiro, and Will Veneble).

Ideally, the Rays trade for a left handed hitter and the need to keep Nava becomes less pressing, but without the impact of a significant trade, it's best if Nava comes back to the Rays. The improvements over 2015 should be real.

Statistics and data are from Fangraphs.