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The Patrick Corbin question: who does he replace?

Patrick Corbin's 15-month return from Tommy John surgery is in its final stages. But when he's ready, it will pose the latest in a thorny line of roster questions. Who does he replace in the rotation?

Mark J. Rebilas-USA TODAY Sports

It's fair to say, the Diamondbacks' starting pitching thus far certainly hasn't been great. Going into last night's contest, they had a 4.69 ERA that ranks 12th in the National League by ERA (4.69) and tied for 12th by ERA- (116). That's slightly better than pre-season projections which had us ahead only of the Rockies in this department, but not a major improvement. It is still easily the biggest problem for the team: they are currently ranked 25th in WAR by starting pitching, 11th in relief pitching and 10th in position player performance. Put another way: if their rotation was as good as the offense so far, we'd probably be in the fringes of the playoff race.

As noted, this doesn't exactly comes as a surprise, and this season was always expected to be one of evaluation: what do we have in the rotation going forward? So far, the results have not been good: that 4.69 ERA is a little worse than the 4,44 figure last season - though our rank in the NL has actually improved, because starters overall seem to be having a harder go of it this year. Still, of the pitchers who started Opening Day in our rotation, while there has been a broad range of variation in the individual performances.only one has currently got an OPS+ of better than 83. So, purely on that basis, a rejuvenated Patrick Corbin should be an improvement.

Corbin's return from TJ

The key word there being "rejuvenated". Even if healthy, it would be optimistic to expect Corbin to return to 100% form immediately, considering the last time he faced major-league hitters in meaningful games was September 2013. It will take time. A yardstick for that is perhaps Adam Wainwright, who missed the entire 2011 season after undergoing Tommy John in February. He came back at the start of 2012, and in his first five starts, had an ERA of 6.75; even through the end of June, Wainwright was still at 4.75. But thereafter, he was back to his old form, posting a 3.18 ERA over the second half of the season.

Corbin not coming back so quickly may be helpful in this regard, the extra couple of months allowing his arm strength to be closer to what it was. But we also saw with Daniel Hudson what seemed to be a re-learning curve, even though his raw stuff was still there. He was bringing a fastball in the mid-90's, but through his first 14 games and 17.2 innings since returning to the major leagues last September, he had a 7.13 ERA. I would not expect Corbin immediately to return to the 113 ERA+ form he showed in 2013. The rest of the season should be less about results, more about proving himself healthy, and in a state where he can be join the rotation for 2016 and beyond.

Room will need to be made, unless the team decided to go with a six-man rotation, which seems unlikely - not least because this would probably cost the team the services of a bullpen arm. There might be something to be said for it from Corbin's point of view, reducing the wear and tear on his elbow and giving it an extra day to recuperate. However, would it negatively impact the other members of the rotation? The Mets just abandoned their effort at a six-man rotation, but Rob Arthur crunched numbers and found "a potentially meaningful drop in injury risk." If we're in this for the long haul, more than 2015, it may be worth considering.

Assuming Chip Hale sticks to his traditional guns (based on his refusal to replace Addison Reed with a committee, that seems a reasonable assumption), who might be forced out by Corbin's return? Let's take a look at the five current incumbents. Here are their stats to date, followed by some commentary, in alphabetical order.

Anderson 27 1 1 3.12 11 66.1 66 23 23 3 15 47 130 3.14 1.221 9.0 0.4 2.0 6.4
Collmenter 29 3 6 5.24 12 68.2 85 42 40 13 10 33 77 5.05 1.383 11.1 1.7 1.3 4.3
De La Rosa 26 4 3 5.84 12 74.0 76 49 48 14 19 71 69 4.50 1.284 9.2 1.7 2.3 8.6
Hellickson 28 4 3 5.29 12 66.1 74 39 39 11 23 49 77 4.87 1.462 10.0 1.5 3.1 6.6
Ray 23 1 1 1.53 3 17.2 15 3 3 1 5 13 270 3.39 1.132 7.6 0.5 2.5 6.6
Chase Anderson

Chase has quietly been an extremely pleasant surprise, and with a FIP almost in line with his ERA (3.14 vs. 3.12), his peripherals suggest this could be sustainable. Anderson having one win in 11 starts shows how meaningless that stat is, if any more proof were needed. How has he become our best starter? According to manager Chip Hale, "that's called pitching... He's mixed his pitches and commanded both sides of the plate - does all the little things well. Is his stuff electric? It's pretty good. I don't think we give him enough credit for having good stuff. You see him throw fastballs by really good hitters. Maybe that's because he sets it up with other stuff."

Josh Collmenter

After a good April, Collmenter has a 7.50 ERA in seven outings, without one quality start. He has been getting blasted, giving up no less than 12 home-runs over those 36 innings [he allowed only 18 all last year, in virtually five times as many IP] Further evidence he's not fooling anyone? A K-rate of 4.3 per nine IP, which ranks Josh dead-last among the 50 qualifying pitchers in the NL. The cut fastball, which he throws two-thirds of the time, is averaging 84.4 mph this year, down 1.5 on 2014. While velocity has never been his thing, there's a point below which deception ceases to work. But where can he go, and is the team willing to demote their Opening day starter?

Rubby De La Rosa

The enigma that is De La Rosa continue to perplex. After he had a couple of really good outings in May, June has been a complete disaster, 16 earned runs being allowed over only ten innings. The main cause of his recent struggles is the long-ball, particularly with men on base: of the four home-runs given up by Rubby this month, all but one have been three-run shots, and only two of the last nine have been solo bombs. This may be bad luck, as his HR/FB rate is up to 13.5%, compared to league average of 7.7%. Among the 106 qualifying pitchers in the majors, only James Shields (14.6%) has a higher figure.

Jeremy Hellickson

Up until last night, had been having a run of decent, if not stunning, outings, but this was a return to the bad Hellickson with who we became familiar in April. He's the most well-paid member of the D-backs rotation, though at $4.28 million, the team was willing to eat more money than that when dumping Trevor Cahill on the Braves. Hellickson was virtually the first signing made by the new front-office, and dumping him would carry a sizable slice of crow along with it. But if the team is serious about building for the future - a future in which Jeremy is unlikely to play a significant role - the starts could be better used in evaluating younger pitchers.

Robbie Ray

Pulled back into the rotation recently as a result of Archie Bradley's assignment to the "disabled list" [quotes used advisedly], Ray has also shown signs of living up to his potential. Obviously, he is not going to have a 1.53 ERA the rest of the way, because he won't continue to leave 91.8% of the runners he allows on base [league average is 72%]. But even if he regresses to his FIP, currently at 3.39, it would still be pretty solid. However, as the last man in, he has least in the way of tenure, with only three starts this season. The uncertainty about Archie Bradley's return may also play into his future.