The numberFire MLB crew has been - and will be - posting feature articles in a series entitled "Buy or Sell."

The concept of this feature is simple: We will examine something currently interesting in baseball, such as a player, team, or statistic and discuss whether we, as a baseball community, should be buying or selling them or it.

There may not always be an easy or clear-cut answer to this question, as streaks and fluke performances are abundant in the game we know and love. With this exercise, we intend to examine such performances and make a case that a performance is either the result of a player getting better at baseball (buy) or mere good fortune (sell).

Not all articles in this series will deal with analyzing a small-sample size performance or a hot streak. Some will deal with the promotion of a top prospect, while others could deal with a specific stat with a specific player, such as @DanWiggles38 or @numberFire) and let us know.

Without further ado, here is the latest edition of Buy or Sell, featuring Astros' starting pitcher Dallas Keuchel.

Background

Formerly a poor pitcher on a poor team, Dallas Keuchel may have been one of the most unlikely breakout candidates in organized baseball. The soft-tossing lefty posted respective ERA’s of 5.27 and 5.15 in 2012 and 2013 respectively, while amassing a very underwhelming 0.3 Wins Above Replacement (WAR) during that time.

While Keuchel’s peripheral statistics did improve slightly during the 2013 campaign, he was still a below average pitcher. This season, however, Keuchel has gone from close to replacement level to close to elite, posting an outstanding 1.9 WAR through 10 starts.

Are his 1.9 WAR, 2.55 ERA, and 0.98 WHIP merely flukes or is Keuchel a significantly improved player? Despite his poor history, there are reasons to believe that Keuchel is indeed an improved player that will continue his hot start.

King of Ground Balls

When looking at his pitch data, one will notice that Keuchel has drastically increased the usage of his two-seam fastball, from 29.6% in 2013 to 40.5% in 2014. What has sparked this change? Well, the effectiveness of the pitch is one good reason.

The metric wFT/C tells us the runs above average generated by Keuchel’s two seamer, and proves that the pitch is significantly better this year. His -0.95 mark in 2013 is below average but his 2014 mark of 2.55 makes it close to an elite offering.

Hurlers with elite two seam fastballs tend to generate lots of ground balls, and Keuchel is no different. He has always been a ground-ball pitcher, but his improved two-seamer has helped his ground ball rate jump almost 11% to a MLB-leading 66.5%.

Even better, his 3.43 ground ball to fly ball ratio is by far the best in the Majors, as no other pitcher is even above 3.0. Keuchel's improved two-seam fastball has turned him into not only a ground ball pitcher, but the best ground ball pitcher in the Major Leagues by a wide margin.

Other Improvements

The improved two-seamer and increased ground-ball tendencies have been the main cause of the breakout, but other aspects of Keuchel’s peripheral statistics confirm the notion that his improvement is legitimate.

The biggest change is that Keuchel has essentially stopped walking opposing hitters, lowering his BB rate from 3.05 to a minuscule 1.53 per nine innings. Equally as impressive, his K rate has not suffered as a result of this, instead rising from 7.20 to 7.77 per nine innings.

The result is an elite K/BB ratio of 5.08, good for ninth in Major League Baseball among qualified starters. If we also consider his home run rate, we can applaud his 2.65 FIP that suggests his 2.55 ERA is justified.

Another metric on the ERA scale is SIERA, which considers the three true results (home runs, strikeouts, and walks) along with batted ball data, so Keuchel is credited for inducing a high rate of ground balls. In this metric, Keuchel ranks third in the league, behind only superhumans Jose Fernandez and Masahiro Tanaka.

The final two statistics that support my case in favor of Keuchel are his HR/FB rate and line-drive rate. The first, HR/FB rate, is simply a percentage of fly balls induced by a pitcher that are hit for home runs. This is a statistic that is subject to significant random chance and is generally an unsustainable skill, but Keuchel’s HR/FB rate of 10.8 is very close to the traditional league average figure of 10.5%. This means that his low home run rate is solely the result of of his ability to keep the ball out of the air and is not the result of good fortune with balls put in the air.

As for line-drive rate, his 14.1% mark ranks second in MLB, behind only Marco Estrada of the Brewers. Line drives obviously often result in hits, so this low number supports the legitimacy of his low .221 batting average against.

Buy or Sell?

While the lack of name recognition may have resulted in many writing off his hot start, there are many reasons to believe that Keuchel is here to stay. Nothing about his performance thus far suggests that his performance is a fluke, so we would be foolish to simply write him off because we have not heard of him or do not know anything about him.

Inducing ground balls, limiting fly balls, striking out opposing hitters, and refusing to walk opposing hitters are all sustainable skills, and Keuchel has demonstrated each of these skills this season. There is no reason to believe that these skills will go as fast as they came, thus we ought to buy the notion that Keuchel is simply a significantly improved hurler.

This is not the same replacement-level pitcher we have seen in Houston over the past two years. This is an elite ground ball pitcher with an elite K/BB ratio who is here to stay. He has made obvious improvements in multiple facets of his game, and we have every reason to believe that these improvements will be sustained in the future.

Verdict: Buy