The Inside Story on Jeff Locke

Jeff Locke has made the leap from fifth starter to Pirates ace in a few short months, anchoring the NL Central leader's starting rotation while A.J. Burnett and Wandy Rodriguez heal. The lefty takes the mound tonight against the Oakland A's with a 2.12 ERA, trailing only Clayton Kershaw among qualified starters. Locke has been better at preventing runs than Stephen Strasburg. Better than Matt Harvey. Better than Adam Wainwright. Not bad for a guy battered for a 5.82 ERA in short stints during the 2011-12 seasons and dubbed "The Intern" by manager Clint Hurdle during spring training.

Whether Locke's success continues, however, is much less clear. His ERA is sparkling, but he doesn't induce a lot of strikeouts (6.1 per nine innings pitched) or limit free passes (3.9 BB/9). His Fielding Independent Pitching (FIP) -- what you'd expect his ERA to be based on Ks, walks and home runs allowed -- is 3.86.

The disconnect between Locke's expected and actual results is most pronounced when he throws inside -- supposedly a cardinal sin for soft-tossers. Few do it more often -- or with more success.

Locke looks like the stereotypical "crafty lefty" who avoids confrontation at all costs. He's on the small side, standing six feet and weighing 185 pounds, and he only tops 90 MPH with a gust of wind at his back. Despite his so-so velocity, the Pirates lefty has thrown more inside fastballs (47% of his total heaters) than any National League starting pitcher this side of Scott Feldman (48%), now in the AL with Baltimore. Among AL starters, only Derek Holland (55%) challenges hitters inside more often. Locke's thriving on the inner third, too:

Locke's opponent slugging percentage on fastballs vs. left-handed hitters

Locke's opponent slugging percentage on fastballs vs. right-handed hitters

Locke has limited hitters to a .186 slugging percentage when he tries to jam them with a fastball. That ties him with Cliff Lee for the third-lowest mark in the majors, trailing just flame-throwers Harvey and Jose Fernandez.

Lowest opponent slugging percentage on inside fastballs among SP (min. 50 PA throwing inside)

Locke's success in busting batters inside with his fastball is baffling for several reasons:

• Locke has the lowest average fastball velocity (90.1 MPH) among pitchers on the list above, and Lee (90.7 MPH) and Alex Cobb (90.4 MPH) are the only other guys who throw under 92 MPH. Pitchers with Locke's fastball velocity tend to get spanked when they go inside. Pitchers throwing 89-91 MPH fastballs inside have a collective .464 opponent slugging percentage this year, compared to .475 for those throwing 92+ MPH heat.
• Locke hardly ever gets hitters to whiff against inside fastballs. Hitters are swinging and missing just 8.6% of the time, well below the 12.4% MLB average. Even fellow soft-tossers Lee (16.3% miss rate) and Cobb (11.9%) induce more swings and misses on inside fastballs.
• He doesn't back off even when he falls behind in the count, throwing his fastball inside 42% of the time when the hitter has the advantage. The MLB average, by contrast, is 26%. His opponent slugging percentage in such situations is .400, compared to the .585 MLB average.

Can Locke keep thumbing his nose at conventional pitching wisdom, beating hitters inside with not-so-fast fastballs? Or will he get his head handed to him in the second half? Stay tuned as we learn The Intern's ultimate fate.