The Revival of Trevor Cahill

The early struggles

Last year, Trevor Cahill had an up and down season, but finished the season strongly, with a 2.20 ERA over his last eight starts, going undefeated in that time. Hopes that he would continues in that vein - perhaps even returning to the form he had in 2010, when he was an All-Star at age 22 - looked shaky in spring, where he had a 6.95 ERA and was smacked around at a .366 clip by opposing hitters. But, it's just spring training, right? Unfortunately, this was one case where spring numbers were apparently a good predictor of things to come. Right from the off, Cahill struggled, his first outing resulting in Cahill issuing eight hits and four walks in a mere four innings.

Things didn't get better from there: four starts in, Cahill had an 0-4 record, with a 9.66 ERA and 13 walks in 17.2 innings, and the day after his fourth outing, the team announced he would be moved to the bullpen. Cahill admitted there were issues, saying, "I'm just not pitching well. There are no excuses," but was unsure as to the specific cause. "I was getting hit [this spring], but I felt good command-wise. It was probably the best I've felt in two years. That's why I was getting curious as to why I was getting hit, maybe it was sequences or whatever. Once the games started, maybe I was trying to do too much not to get hit. That led to walks and the whole cycle of falling behind."

There was still plenty of movement on his pitches, for sure, but it was unpredictable; the basic problem was nobody knew where Cahill's pitches would end up. That included the hitters - Cahill was still striking out very close to a batter per frame (17 in 17.2 IP) - but also Cahill. According to Towers, the move to relief would hopefully "take a little pressure off of him. You can almost tell out there, I mean trying to execute pitches. Trying to go away and it goes inside. Trying to go inside and it goes away. It's tough when you're going through what he's going through. But with him in the bullpen, I think the good thing for him is that he doesn't know when he's going to pitch."

Seeking relief

Between April 18 and June 6, Cahill made 15 appearances out of the bullpen and, in general, pitched pretty well, with an ERA of 3.04 over 23.2 innings. His strikeout rate remained good (27 K's), though there were still a few too many walks (12). Initially, he was used in a longer relief role, his first seven outings averaging 33 pitches, but this seemed to tail off, with the next eight covering only nine innings in total. It may have been this, rather than poor performance - as noted, his numbers weren't bad by any means - that spurred the decision to send him to the minors, to get him stretched out again, ready to start.

Getting his agreement for the demotion was probably fairly easy, as Cahill didn't seem to like his new role as a reliever, but bit the bullet. Trevor said after taking the loss against St. Louis on May 21, "It's tough out of the bullpen. As a starter, if it was the second inning or whatever, the ball (Allen) Craig hit (with the bases loaded in the 12th inning) might have been a double play. I could have gotten out of it, minimized damage and went on to pitch a decent game. But as a bullpen guy, your margin for error is so small."

Still, it was a shock on June 9 when the team announced he had been designated for assignment. Usually, this is the baseball equivalent of being fired, but in this case, Kevin Towers said, "There's a gameplan in place for what we're ultimately going to do... Because of service time and where he's at, there's a lot of hurdles and hoops you've got to jump through." One of these was Cahill's agreement, but given his desire to start, it appeared he realized he must go down, to come back to the rotation. Right now I'm not built up. I'm sure they've got a plan and I trust them and I feel like they'll do right by me... I want to stay here, but I want to get better and be the guy that I can be."

Minor endeavors

Cahill made one start for the Visalia Rawhide in High-A, and then six with the Reno Aces. The results were mixed. He did hold opponents to a .217 average against, and a 4.45 ERA was certainly an improvement over what he posted when starting in the majors. However, there were still concerns over his ability to spot his pitches, with a total of 20 walks in 30.1 minor-league innings. But, it was clear Cahill was being stretched out in a low-impact environment. He threw 41 pitches in his first game, increased that count in each of the next three, and for his final three starts, threw between 90-100 pitches.

However, he did also make some mechanical adjustments, adjusting the position of his hands before going into his delivery, though that appeared to be a work in progress, On his return, Cahill said, "Out of the windup I'm feeling pretty good. It's just the stretch wasn't very consistent. I went back to in between where I started (setting up my hands) and where it used to be. Hopefully it works out."

Back in the rotation

His first start back in the major leagues, on August 18th, lasted only five innings, though part of that was the team being behind and needing offense when his turn at the plate came up. He allowed three runs, all in the same inning, and said following the game, "I walked a guy and he scored. After that, I let my stuff work. A lot of that is being in the bullpen when you come in and throw your best stuff at them. As a starter, you've got to pace yourself and know what kind of pitcher you are. Sometimes you get greedy, but you can't."

His next start lasted only four innings, though Cahill was somewhat the victim of his defense, with four of the seven runs allowed being unearned. But that outing and the one which followed did mark an apparent turning point in one big way: it was the first time in Cahill's entire career, he had made consecutive starts without issuing a single walk. Admittedly, at only 10 innings combined, he wasn't pitching deep into games, but as Cahill put it, "Anytime I feel like I can throw the ball somewhat where I want to, I feel a lot more confident. It's tough when you're throwing and your stuff is kind of going all over the place. You start competing against yourself more so than the other team."

The four outings since then have been definitely encouraging: Cahill has pitched into the seventh inning, each time allowing two earned runs or less. His team-mates have expressed cautious optimism, Miguel Montero saying, "I'm excited by what I'm seeing so far. He's been pretty good. I mean, obviously, it's a work in progress and we want him to get the confidence level up again." Aaron Hill added, "Once he gets a few of those outings in him, he'll realize he has great stuff... He's got to know he's got one of the best two-seamers in the league. If he can establish that and work off his sinker, it's going to be fun to have him back to what he could be and what he knows he could be."

What's changed for Cahill?

Let's take a look first at some stats and see if we can see what's changed. We'll divide his season into three section: initially as a starter, during his time in the bullpen, and after his return to the rotation. Of course, sample size on all these is going to be troublesome, so bear that in mind.

Damn, Cahill was really unlucky early: a .415 BABIP is more than a hundred points higher than you'd expect. Combine that with a control problem leading to too many free passes, plus a home-run rate close to twice what it's been over the past five years, and there's your explanation for that awful ERA. All these have been significantly improved. He got the walks down in the bullpen, and even further on his return: the BABIP has also trended that was, and he has only allowed one home-run over seven starts. The last probably is an over-correction, but one wonders, if we'd simply waited Cahill's issues out, how much of this would have corrected itself?

A couple of other thoughts, I note a sharp spike in the groundball rate, but conversely, also a sharp uptick in the line-drive rate off Cahill since he returned to the rotation. This would suggest hitters may be making better contact with his pitches. He's throwing more strikes but getting fewer strikeouts. Perhaps this is tied to the lack of walks, with Cahill consciously trying to rein in the amount of movement on his pitches, and show better control. While that would reduce the number of walks, it would likely also reduce the number of swing and misses, and thus the K's. To find out if that's the case though we need to dig deeper into the numbers.

Special f/X

Next, let's compare his repertoire during his two spells in the rotation - in this case, I'll omit the bullpen work, because, as Cahill found out, relieving is a very different animal. Courtesy of the wonderful BrooksBaseball.net, here are the breakdowns, first for Cahill's four starts at the beginning of the year, and then for the seven since he came back from Reno.

There are readers who are frozen in terror, like deer in headlights, by the above. It's okay. I'm here. And I will talk you through this. The first column is the kind of pitch. The next three are the raw number of times that pitch was used, the percentage of use, and its average speed. Comparing the before and after, we see that Cahill has become more of a two-pitch guy. The sinker is still his bread-and-butter, but even more than it was, and there has also been a sharp increase in his change-ups. Combined, these two now represent 84% of his pitches, compared to 72% before. His four-seamer has almost disappeared, and the curve is also less common.

The increase in change-ups is something which was discussed earlier this month, in particular mentioning its use against right-handed batters. "It was so hit-or-miss (before), I guess. If I don't have that pitch, I feel like that's kind of my equalizer. I can throw it behind in the count or to the more aggressive lefties if I've got a good feel for it. Throwing it to righties too adds a whole 'nother dimension." When he was pitching in April, he only used the change-up 9.5% of the time against right-handed bats, compared to 24.3% of the time versus southpaws. Since his return, the same figures are 15.7% and 29.7%, so he has increased its use to both, but indeed, particularly to righties.

The following column across is velocity. There's not much difference between before and after, with all his pitches having a little less "oomph" on them. However, I do note the gap in velocity between Cahill's sinker and change has increased by about 5%. That's generally a good thing: it's generally the difference between a pitcher's fastball and his off-speed pitches which is responsible for flummoxing a batter, who is expecting one and gets the other. The less similar they are, the greater the chance of a swing and a miss or weak contact. So, this is perhaps a factor in Cahill's impreved effectiveness.

Next, are data for movement by the pitch, and interestingly, appears to show Cahill's sinker is moving a little more than it was before he was sent down, against what I speculated above. There's no denying the copious amount of break + drop Cahill gets. Horizontally. the August figure of -10.19"  ranked Cahill's sinker fifth among all pitchers throwing it at least 100 times that month. For vertical movement, where a lower figure means greater drop [for reasons which this pic may help explain], he was 7th of the 52 qualifying pitchers. Cahill's sinker may not sink as much as Brandon Webb's, which had a VMov of just 1.06, but it breaks more horizontally (Webb was at -8.68).

Finally, there's the release point, which again has two components, horizontal and vertical, depending on where Cahill's arm was, high/low and 3rd/1st base side of the rubber when the ball was released. For these, it's probably easier to visualize if we plot each of these month by month, so you can see the changes over time for his three main pitches (sinker, curve and change-up). It would take someone with better knowledge of pitching mechanics to look into these, but you can see that Cahill does appear to have been adjusting his delivery, resulting in changes over the season for his release point.

And what of the future?

Trevor is under contract for next year, with two seasons of team options beyond that. At $12m, $13m and $13.5 million, they aren't cheap, but considering Bronson Arroyo will cost either $23.5m for two years or $34m for three, it's by no means excessive, if Cahill can reach decent form. Cahill probably has seven starts left. If these cover 45 innings and 15 earned runs, he would basically match his 2013 ERA. That may not seem like much, but considering the truly wretched start, counts as a pretty impressive comeback. It would require an ERA of 3.00 down the stretch, but his four August starts have resulted in a 2.33 figure with a 2.84 FIP, so it's not impossible.

The keys will be what has helped power Cahill's recent success, with his August ERA ranked 29th among 116 qualifying pitchers and his FIP is 25th. Really, it's pretty simple: don't walk people, keep the ball in the park and generate ground-ball outs. If he can cut back on the line-drives too, that would help his BABIP drop back toward what is expected. Having a solid Cahill upon whom we can rely, would certainly be a boost to the Diamondbacks rotation in 2015 and beyond.