The new and improved Erasmo Ramirez

As spring training progressed and more Rays pitchers went down with injuries, it was clear that the Rays needed to make a move to get help in the rotation. Their answer was to send former first round draft choice Mike Montgomery to Seattle in exchange for long reliever Erasmo Ramirez.

Ideally, the Rays would only need Ramirez for two starts, and then could transition him back into a swingman role. Alex Cobb and Drew Smyly were slotted for early returns from the disabled list, but as we all know, the Rays' luck took a turn for the worse (Tommy John, a labrum tear), and the Rays needed to rely on Ramirez to fill a bigger role.

With Seattle, Ramirez had moderate success. Entering the league at age 20, he posted strike out rates that were close to league average, but trouble limiting home runs and walks ultimately pushed his ERA up toward 5.00.

Some of these home run troubles were driven by a high HR/FB rate, so his xFIP suggests that he got "unlucky;" however, allowing a lot of fly balls in general (like Ramirez did in 2014) will make him susceptible to these stretches of "bad luck."

After his acquisition, Erasmo made one sterling start to conclude Spring Training, but the start to his career as a member of the Rays was forgettable. In two appearances, he allowed 15 earned runs in only 5.1 innings and walked six. The Rays shifted him to the bullpen and used him in low leverage situations. Ramirez shined in this role, and was moved back to the rotation in the middle of May.

Since then, Ramirez has ripped together a string of exceptional starts, posting a 2.52 ERA over that span and curbing his homerun problem. His performance has exceeded all expectations, but is it sustainable?

Even though it might seem like he is obviously over-performing, it is more important to identify what is causing the recent hot streak. From there, we can determine if this is completely a fluke, or if his underlying skills are changing as well.

Photo credit: Jennifer Nicholson-USA TODAY Sports

In Ramirez's case, there are a few aspects of his performance that are causing this recent hot streak, and all have varying degrees of legitimacy.

Mixing It Up

Before the start of this season, Ramirez had thrown his curve 7.92% of the time. Despite its -2.77 inches of vertical movement and velocity gap of nearly 14 mph, it was largely ineffective. It generated fewer whiffs than league average, and posted a 28.57% groundball rate, which is much lower than the league average of 48.7%. While it was thrown infrequently, hitters took advantage and posted a .597 slugging percentage on his curveball.

Once he was traded to Tampa Bay, however, his usage on the pitch dropped to 2.26%. The Rays seem to have identified his curveball as a weak spot in his arsenal and instructed him to throw it less.

As a result, Ramirez has been throwing his fastball and his change up, more often than in past seasons. And rightfully so, his change up's shape is conducive to generating high rates of ground balls, and has drawn whiffs on 41% of opposing hitters' swings (league average is 30%), making it his best pitch.

While he has historically used his changeup against left handed hitters, he has integrated it into his attack against right handed hitters this season, as Ian predicted the Rays would ask of Ramirez. Consequently, it has been exceptional in a small sample size, and helps explain how Ramirez cut down opposing righties' wOBA by nearly 30 points from last year.

Overall, the logic here is very basic: throw the good pitches more often, and the bad one less. The adjustments might have taken some growing pains in his first two outings, but it has helped Ramirez be a more effective pitcher.

Even if other aspects of Ramirez's performance regress and cause his ERA to rise, the change in pitch mix is likely to stay and continue to make Ramirez a better pitcher. So is it sustainable?

The Secret Weapon

Giving up on a pitch (the curve) isn't always the best answer for pitchers, but in this case it has been beneficial, because Erasmo has one more piece to round out his arsenal.

While Ramirez's change up has been excellent, he has gotten the best results from his slider. Against right handed hitters, whom he usually uses it against, Erasmo has a 45.1% whiff rate and a 55.6% ground ball rate. This is an extreme deviation from his historical performance, where his slider was previously a below average pitch that got 29.2% whiffs and generated ground balls at a 30.6% rate.

Looking at the components of his slider, we wouldn't expect it to be elite.

It has below average vertical movement, and isn't fast enough to be considered a "hard slider" (like Chris Archer's, for example). Because the pitch shape has stayed consistent from past seasons to this season, I'm very skeptical that his slider has improved. I would expect his whiff rates to move back to his career average, and downward regression in his groundball rates as well.

Batted Ball Tendencies

In addition to changing outcomes on specific pitches, Ramirez has also changed the relative distributions of batted ball types allowed.

During his first two seasons, Ramirez didn't seem to have a specific batted ball tendency - his fly ball and groundball rates were both near league average. He started to shift toward being a fly ball pitcher in 2014, as his fly ball percentage rose from 36.1% in 2013 to 43.2% in 2014. This tendency would fit well at Tropicana Field, which sports a 95 park factor for home runs.

However, Ramirez's batted ball results have switched again this season.  His groundball rate has climbed more than ten percent, from 37.7% to 47.9%.

Throwing more change ups doesn't account for this large of a difference, and because his pitch shapes have stayed consistent, the increase in ground balls would have to come from a shift in pitch location for it to have some legitimacy. Below is a graph showing the vertical pitch location for all of Ramirez's pitches.

Throwing pitches lower in the strike zone would cause Ramirez to theoretically generate more ground balls. This would make it more challenging for hitters to get underneath the pitch and lift the ball in the air, and instead cause more contact on the top half of the ball.

As shown by the graph, Ramirez has been throwing his slider lower in the strike zone, but his other pitch locations have been consistent. These differences are not large enough to support the dramatic change in groundball rate.

Going forward, I would expect his ground ball rate to decrease to the low 40's. Throwing more change ups will help him get more ground balls than previously, though, so regression back to 2014 is unlikely.

Conclusion

In the end, analyzing all of these aspects of his performance may just be nitpicking. While "Erasmo the whiff-getting groundball-inducing pitcher" has been fun and exciting, the Rays probably weren't expecting that type of production.

Reducing the number of curve balls he throws will continue to be beneficial, but the slider's production in exchange is the likely culprit for the unexpected hot streak.

While his whiffs and ground ball rates should come down over time, a 4.25 ERA, 7.0 K/9 starter will still be helpful for the Rays. It's exciting to watch him pitch this well, so for now, I'm just going to sit back and watch, no matter how unsustainable it might be.