Obviously, Arizona general manager Kevin Towers was expecting better results after signing McCarthy to a two-year, $15.5 million contract this offseason. The good news for Towers and the Diamondbacks is that McCarthy should start experiencing some success soon.
His 4.07 Fielding Independent Pitching (FIP)—an ERA estimator based on strikeout, walk and home run rates—is more than three runs below his ERA.
The reason for the discrepancy between his ERA and FIP is the fact that he's allowed a .387 batting average on balls in play (BABIP).
Batting average allowed on balls in play isn't entirely attributable to random luck, as some would suggest. Having good command should allow a pitcher to prevent hard contact, and thus gain more control over what happens when the ball is put in play.
That said, McCarthy should finish the season with a BABIP closer to his .288 career mark than the current monstrosity.
I watched McCarthy's last start against the San Francisco Giants, and he made plenty of location mistakes up in the zone that deserved to get hit hard. However, some regression to his career mean is certainly coming—particularly if he can start to drive the ball down in the zone more often.
When McCarthy pitched for Oakland, he consistently located the ball with good tilt in the lower half of the strike zone. He has the ability to get downward plane on his pitches because of his tremendous height (6'7"). That ability to pitch in the bottom half of the zone allowed him to prevent damage on contact with Oakland better than he has so far this season.
McCarthy can also get some control over what happens on balls in play by changing speeds more. Pitching is partly about upsetting the timing of hitters. That's something he didn't do a good job of against the Giants.
He failed to change speeds and upset their timing. Watching his start, I wondered aloud why he wasn't throwing more offspeed stuff. McCarthy later confirmed that was an adjustment he needed to make sooner in the game.
According to the PitchFX data available at Brooks Baseball, McCarthy threw only four offspeed pitches in his start against the Giants. He threw 50 cutters, 33 sinkers, three curves and just one changeup.
His failure to change speeds allowed the Giants to sit on hard stuff all night. They took advantage with eight hits, four runs and two home runs off of McCarthy in his six innings of work.
It wasn't all negative for McCarthy against the Giants. He struck out six, walked only one and was in line for the win until the Arizona bullpen imploded.
He also showed a good understanding of how to attack the Giants' hitters. He shut Buster Posey down by busting him in with sinkers all night. He attacked Brandon Belt's weakness on the inside part of the plate with hard cutters in on his hands. He struck out the free-swinging Pablo Sandoval with an eye-high fastball.
Clearly, McCarthy understands how to pitch to the weaknesses of his opponents.
In his two seasons with Oakland, McCarthy put up a 3.29 ERA to earn his free-agent contract with Arizona. His stuff is just as good as it was with Oakland. In fact, his velocity is actually up a bit from last season.
His strikeout-to-walk ratio is also better so far this year than last season. His current walk rate is the fifth best in baseball.
The reality is that any pitcher can look bad over a six-start stretch. Matt Cain, Roy Halladay and Gio Gonzalez are with McCarthy at the bottom of the ERA leaderboard in 2013. When the season ends, all four of those pitchers should be much closer to the top, given their track records.
Based off his last start against the Giants, McCarthy will need to change speeds and get the ball down in the zone more to improve his ERA.
By season's end, his ERA should be well under 4.00. If that happens, Towers will be vindicated for his offseason investment.