"He's legit," assessed Randy Smith, the Padres' director of player development at the time, following the three-team trade on July 31, 2010, that sent unknown minor league pitcher Corey Kluber eastward to Cleveland. "His slider is a strikeout pitch. He could be a middle guy or at the back end of the rotation."

Kluber, a fourth-round pick out of Stetson University who never cracked either organization's top 20 prospects, is now one of the players on the American League's final player ballot for the All-Star team after going 8-6 with a 2.78 ERA and 137 strikeouts in 125.2 innings so far. He keeps some other rarefied company: Among pitchers with at least 270 innings since the beginning of 2013, Kluber is one of just four to post a strikeout rate of at least 9.0 K's per nine innings and a walk rate below 2.2 BB/9. The others? Arguably the top three starting pitchers on the planet -- Felix Hernandez, Clayton Kershaw and Chris Sale, who have a combined 11 All-Star appearances and nine top-10 finishes for the Cy Young Award (including three winners).

Or how about this? Only Stephen Strasburg, David Price and the Tribe's budding ace have averaged at least 9.8 K/9 and fewer than 2.2 BB/9 this season. Kluber, by the way, leads the three with his 2.86 ERA and a 2.65 FIP (fielding independent pitching).

The 6-foot-4 right-hander's meteoric rise is something the Indians did not see coming; the club left him off its Opening Day roster last season, only to recall him after a Ubaldo Jimenez implosion sapped the pitching staff.

So how did Kluber go from obscurity to an All-Star-worthy pitcher? Well, as Smith predicted following the trade, a lot of it has to do with his secondary offerings, but it's not just his slider. It's been the development of his third pitch, a lethal curveball, that's pushed him skyward.

According to ESPN Stats & Information, the opposition has hit .080/.112/.107 against his curveball while striking out 57.3 percent of the time against the pitch. To put that into perspective, hitters have a .146/.169/.222 triple-slash line against Adam Wainwright’s curve, largely recognized as one of the best in baseball.

The pitch also has the largest amount of horizontal movement of any curveball in the game -- a staggering 10.9 inches (Wainwright's averages 8.8 inches). And then there's the aforementioned slider. Opponents are hitting just .231/.265/.323 against it this season, while swinging and missing 33.7 percent of the time. Of Kluber’s 137 strikeouts, 103 of them have come via the curve or slider.

And here's where it gets a little ... weird.

His fastball, despite averaging 92.9 mph (tied for 21st highest among 95 qualified starters), has been hit to the tune of .345/.397/.518, basically the same line that won Ernie "the Schnozz" Lombardi the NL MVP in 1938. The trend, however, has existed throughout Kluber's career: Hitters have a .348/.405/.542 triple-slash line against his fastball since his debut in 2011.

As for the problem, it appears he's rather predictable against southpaws, who have hit .374 against Kluber's fastball in 2014 with 16 extra-base hits in 107 at-bats. Here are his fastballs against left-handed batters:

ESPN Stats & Info

The overwhelming majority of Kluber's fastballs to left-handers have been low and away, or away and off the plate. The difference in production is quite noticeable when he does pitch inside, however: Left-handers are hitting .189/.338/.358 against him on inside fastballs since 2013.

Kluber's terrific numbers -- 125.2 IP, 3.4 fWAR, 26.6 percent K rate and 5.8 percent walk rate -- earned him consideration for the All-Star Game. He's been one of the best pitchers in the league. The question: Would he be even better if he were challenging left-handers more on the inner part of the plate? That's the unknown. A lot of pitchers have made a good living by living on the outside corner to lefties, so you can't automatically fault that approach. Maybe Kluber isn't comfortable pitching inside. Maybe his fastball lacks the proper deception and late movement.

Pitching inside more is something to consider though -- and a scary thought for opponents that Kluber has room for improvement.

Joseph Werner writes for the It's Pronounced "Lajaway" blog on the Indians.