Who Will Patrick Corbin Be?

There’s no debate about the fact that Patrick Corbin had a fantastic year in 2013. He was clearly the anchor of a Diamondbacks staff that was otherwise tough to figure out. And not tough to figure out in a good way, where hitters didn’t know what was coming. Rather, the rotation was tough to figure out because it lacked consistency. Patrick Corbin, however, was pretty darn consistent and without him, last season would have been even tougher to watch.

Considering that Corbin was never a top prospect, his 2013 is somewhat surprising. I can’t find him ever ranked higher than 6th in the system when he was a prospect and most comments have him pegged as a guy with good command but mediocre stuff. The ‘mediocre’ tag is usually a result of his lack of velocity as a prospect, typically described as sitting right around 90 with his heater. In his sophomore season, Corbin showed his growth and strength by averaging nearly 93 with his fastball, which is pretty solid from the left side. Although he ran out of gas in the final two months of the season, 2013 was clearly a success for him.

But that’s who Patrick Corbin was, not necessarily who he will be. It’s important to know whether or not Corbin is a nearly 4-win player going forward or if he’s in line for some regression. The first place to look was is whether or not his peripherals supported his ERA. To accumulate these, it’s most simple to compare his ERA, FIP and xFIP. The results are surprising:

• ERA: 3.41
• FIP: 3.43
• xFIP: 3.48

Surprising, right? And, lucky for Diamondbacks fans, surprising in a good way. There’s nearly no variance between the numbers, suggesting that Corbin’s results were not luck-based. A quick glance of his BABIP shows that hits fell in at a slightly-lower than league average rate for Corbin, but that’s partly due to him having the league’s best defense behind him, not entirely that he was lucky.

At just 24, and with only two major league seasons underneath him, Corbin still has room to grow. His two-seamer and slider were incredibly effective last season, especially against lefties. He held same-handed hitters to a .253 wOBA in 2013 but was vulnerable to righties who put up a more robust .310 wOBA. Granted, a .310 wOBA doesn’t mean that he got ‘destroyed’ by right-handed hitters, but he clearly had a split between right and left-handed hitters.

What’s behind behind that split? The changeup. His slider runs away from left-handed hitters while it breaks towards righties. This is a risky proposition and I can remember vividly at-bats where Corbin struggled to put away right-handed batters because they could foul off the heat and lay off sliders down in the zone. With a developed changeup, however, he could have ended these at-bats more quickly and with more success. Because the change breaks away from righties, similarly to his two-seamer, it’s more likely to draw whiffs and weak contact. This is the weapon that Corbin needs if he’s going to maintain the success or even take a step forward.

For what it’s worth, Steamer projections have just been released on FanGraphs and that system has him worth 2.9 WAR next season. The bulk of the decrease is due to a projected drop in innings pitched plus a rise in BABIP closer to league average and, to be honest, it’s probably more likely that Corbin is 3-win player next season. Predicting 200+ innings is dangerous given the frequency of pitchers’ injuries and his BABIP is likely to rise somewhat.

But the one thing that can reverse this projection is his ability to harness the changeup, and to me, that’s what Patrick Corbin’s success going forward hinges on. As the season wore on, hitters began to lay off the slider, especially righties. He needs one more weapon to keep them off balance and if it can just become an average offering, he’s got a chance to repeat his nearly 4-win season. If it becomes a great pitch, he has a chance to be one of the better lefties in the league because Patrick Corbin with a average or better changeup is a different pitcher than Patrick Corbin without one.