Last season the Rays became an entirely different sort of team on offense, eschewing their power and strikeout approach for a more contact oriented team that both got on base more often and won games more often.

The Rays won 90 games with their new approach, and were the last team in the American League eliminated from the playoffs. Since the season ended, the team has continued to lean into the power-less approach by acquiring Yandy Diaz for Jake Bauers, and by skipping Nelson Cruz despite a relatively low cost salary.

A team eschewing power in the AL East is curious. Why was this approach been more successful?

One if by land, two if by ground ball

Last Friday, Alex Chamberlain’s “2018 Statcast Park Impacts” article dropped on FanGraphs, where Chamberlain was looking to use wOBA and xwOBA to dig into which parks consistently saw hitters under/out-perform their “expected” results.

There are limitations of using “xwOBA-wOBA” for analysis, most notably due to struggles with hitters on either extreme of the speed spectrum, but theoretically, taking a team-wide look over the past three seasons should cull out some of those weaknesses.

That’s why it was so interesting to see a very specific area in which Tropicana, and by extension the Rays, stand out: success on ground balls.

Here’s a look at the chart, once again from Alex Chamberlain at FanGraphs:

Although the Trop finished behind Globe Life Park in Arlington for the most recent season, no stadium has had the same, sustained, overperformance when it comes to results-above-expectations for the past three seasons as the Trop.

In fact, there are only three other cases of stadiums consistently outperforming expectations on a ball in play result over the past three seasons: fly balls in Colorado, fly balls in Cincinnati, and line drives in Colorado. Tropicana Field alone is a groundball paradise.

Coors Field and the Great American Ballpark are notorious for the success fly ball hitters find within their confines, and line drive hitters go to the vast, open outfield of Coors when they pass away instead of going to heaven.

The Trop, however, has no such reputation for ground ball hitters. Yet, alongside those two stadiums, it has been among the most consistent place for hitters of a certain batted ball type to succeed.

Potential Causes

The first potential cause when looking at any trend over just three seasons of a park stadium would be the roster of the home team. If a team is loaded with speedsters who are destined to see their wOBA exceed their xwOBA, it could throw a wrench in the numbers, writ large.

However, as any Rays fan would suspect, that theory doesn’t hold much water in the Rays case, as the roster has see more turnover than your local pie shop in the past three years.

The roster favored line drive hitters in 2018, but this was fresh off a season in which the Rays seemingly favored power over gap-to-gap production. If there has been one overwhelming trend to Rays rosters over the past three years, it’s that they tried all sorts of approaches in their lineup.

As such, the Rays roster seems an unlikely source.

One other potential cause for this higher wOBA than xwOBA (which, again, would imply that players are consistently getting “lucky,” and players getting “consistently lucky” means maybe it isn’t luck as much as some other factor) is if the Trop turf is playing fast.

When I reached out to our resident theorist JT Morgan on why he thought this phenomenon might be occurring, this was his top theory. The Rays actually swapped out their turf three years ago, which is both interesting and frustrating. It is interesting because it absolutely means this could be a leading cause. However, because the data Alex put together covers exactly the same time as the “new turf” there’s no way to see what results the Rays were having beforehand to know if this “new turf” was any different than the “past turf.”

It still seems likely the turf in general is the most likely cause for the Trop’s extended run of being a great stadium for ground ball hitters, though. Credit to the Rays for leaning into this to finally find success again on offense.

What Does It Mean for 2019

Of the Rays hitters to collect at least 50 plate appearances in 2018, five players boasted ground ball rates of at least 50 percent: Christian Arroyo (70.3%), Matt Duffy (54.3%), Wilson Ramos (52.6%), Willy Adames (52.1%), Daniel Robertson (50.7%). Ramos won’t be with the team in 2019, of course, but the good news is that the other four hitters will be, with Duffy, Adames, and Robertson all likely to big contributors to the lineup, and Arroyo as more of a wild card (that figure would not be sustainable over a full season).

Among Rays pitchers with at least 20 innings pitched, there were six who had ground ball rates lower than 40 percent and another six with ground ball rates over 50 percent.

Before we get to those names, let’s pause to discuss a quick tangent: Typically, when analyzing hitters but especially pitchers, expecting a higher rate of production on offense to correlate with higher groundball rates is the opposite of what we are looking for. Batters should elevate their hard hit balls, and pitchers with high ground ball rates are often prized for limiting offensive production. So, when looking at the names highlighted in this article, keep that in the back of your mind.

Here are the six pitchers with ground ball rates lower than 40 percent, i.e. pitchers who, if the Trop maintained its current run, could potentially be expected to outperform their numbers because of limiting ground balls (again, this is weird compared to normal pitcher analysis): Vidal Nuno (28.6%), Jamie Schultz (29.0%), Ryne Stanek (32.7%), Jake Faria (34.4%), Sergio Romo (36.4%), Ryan Yarbrough (38.0%). Nuno and Romo were granted free agency and Schultz was just traded, but Stanek, Faria, and Yarbs should all play significant roles for the Rays in 2019. It’s also interesting to note that all three of those pitchers have posted lower ERAs than might be expected based on their FIP in their Rays careers. Digging into individual wOBA-xwOBA don’t show as big a difference, but Faria (despite the poor results), was among the Rays pitchers who “got the luckiest.”

The flip side of that group is the following sextet of pitchers with a ground ball rate of 50 percent or higher: Andrew Kittredge (50.4%), Matt Andriese (50.6%), Jalen Beeks (50.8%), Alex Colome (54.5%), Jose Alvarado (55.0%), Adam Kolarek (59.1%). As noted before, having a pitcher with a high ground ball rate is hardly a bad thing, but it’s worth noting that Kittredge, Colome, and Kolarek were the Rays with three highest ERA-FIP gaps, and all six of these pitchers finished with a higher ERA than FIP. (Among the low ground ball pitchers, it was a 50-50 split.)

When considering who the Rays might turn to out of the bullpen, it’s interesting to see that Tropicana Field may have a larger influence on Cash’s selection process than previously suspected. Unique among stadiums, it may not be so simple to call the Trop a “pitcher’s park” any more.

The Big Caveat

Now it’s time for the big caveat to all this information. The Rays are changing their turf again this winter, “exchanging the current turf for a new Shaw Sports Turf product, designed to withstand the myriad events held at Tropicana Field throughout the calendar year.” Given that the turf was the leading theory backing this ground ball production at the Trop, this is clearly noteworthy.

On the flip side of that, there’s also the distinct possibility that the turf they put in this offseason will be as (theoretically) fast as the last batch.

Either way, in this case, the Rays (and their opponents) success on ground balls is something to watch in 2019.