How Corey Kluber Emerged as One of the Best Pitchers in Baseball

A little over five years ago, Corey Kluber was a relatively unknown pitcher in the San Diego Padres farm system. Drafted in the fourth round by the Padres out of Stetson University in 2007, Kluber never really impressed as he moved through the Padres and eventually the Indians farm system.

But that Corey Kluber is long gone. Kluber pitched himself into becoming the Indians ace, and hasn't looked back. In 15 starts this year, Kluber is 6-4 with a 3.35 ERA, 2.69 FIP and 2.85 xFIP. He's striking out 10.06 per nine innings, while only walking 2.65 batters. His 10.06 K/9 puts him fifth-best in baseball, better than Masahiro Tanaka, who won the AL Pitcher of the Month in May over Kluber.

Tanaka's and Kluber's Performance in May

It all started in 2013, when things started to change for Kluber. He was brought up midway through the season and finished the year 11-5 with a 3.85 ERA, 3.30 FIP and 3.10 xFIP, with 8.31 K/9. These numbers weren't spectacular, but they earned him a spot in the rotation in 2014. And at times during the 2013 season, Kluber looked dominant, almost like an ace. In two appearances against the Detriot Tigers in July and August, while both no decisions, Kluber allowed just two runs while striking out 16 and walking just two.

Looking further at his 2013 numbers though, Kluber had a chance to be something really special. To start, he left 72.9 percent of the runners he faced on base. While an average number for MLB starters, this was 10 percent higher than what he saw in 2012. As pitchers will usually regress to the league average LOB% of around 72 percent, Kluber's low LOB% proved he pitched better than his 2012 numbers show, and that he had the potential to improve. Further, Kluber was striking out 22.4 percent of hitters he faced, which would put him in the top 25 in that category, if he had the innings to qualify.

Finally, Kluber's stuff was just nasty. He was getting ahead of hitters, throwing first-pitch strikes 60 percent of the time. Even better, batters were swinging and missing at 10.4 percent of his pitches, numbers that put him with the likes of Zack Greinke and Justin Verlander.

How did Kluber suddenly start pitching like an ace? It all starts with his cutter. Kluber's cutter was one of the best in baseball last year, with a 13.2 cutter runs above average (wCT). Corey Kluber's cutter last year was the second-best cutter in baseball, behind Travis Wood. His cutter was better than Adam Wainwright's and Mariano Rivera's.

To put it into historical perspective, Kluber's cutter in 2013 would have been better than Rivera's cutter in six out of the past 10 years.

Further, the rest of his stuff - a fastball, curveball and changeup - have also been above average. His curveball was 3.2 runs above average in 2013, while his changeup was 1.7 runs above average. The whiff rates on these pitchers for Kluber are also excellent. In 2013, batters whiffed at his changeup 21 percent of the time and his curveball 19.1 percent of the time. Kluber also allows an above average percentage of ground balls, 47.6 percent in 2014 and a below average percent of home runs to flyballs (HR/FB), 8.5 percent in 2014.

This year, his cutter is again one of the best in the league - 7.9 wCT - second-best in Major League Baseball behind Wainwright. Kluber also continues to throw first pitch strikes, up to 65.3 percent of the time from 60.0 percent in 2013, also among the top 10 in the bigs. And batters are continuing to whiff an astounding 11.3 percent of the time - his whiff rates on his best pitches are all up in 2014 as well. Hitters are swinging and missing 23.8 percent of the time on his changeup, and 18.9 percent of the time on his curveball.

To put it simply, Kluber has become one of the best pitchers in the league. He has a 2.57 nERD, a numberFire statistic used to measure how many runs a pitcher prevents compared to the league average per game. Kluber's nERD is fourth-best in baseball among pitchers, only behind Felix Hernandez, Stephen Strasburg and David Price. And it's ahead of supposed better pitchers like Tanaka, Max Scherzer and Yu Darvish.

Kluber's gone from a relatively unknown prospect to a surefire ace for the Indians. And if he keeps putting up these type of numbers, there may be a Cy Young in his future.