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March 12, 2003

The Grand Experiment

Converting Graves and Kim to Starters

by Nate Silver

Sure, the games don't count for anything, and as we've pointed out before, any team relying on spring training to make important roster decisions is likely in for a long season. But there are exceptions, and none more important than in Sarasota and Tucson, where Danny Graves and Byung Kim are bidding to join their respective teams' rotations.

Starting pitching has long been the Bowden Reds' weakest link; 30 league average starts out of Graves would go a long way toward placing them in the midst of a Great American Wild Card Race. The situation is even more critical in Arizona, where PECOTA is expecting a big decline in the Snakes' offense, and the lack of obvious short relief replacements makes the move a higher-risk gambit. If Kim can make the transition successfully, it's not unrealistic to imagine Diamondbacks finishing 1-2-3 in the league ERA race; anything less, and Arizona could have trouble defending its title in what should continue to be a highly-competitive division.

Moving a top-notch reliever into the starting rotation is neither a new nor a particularly unusual idea. The Indians and Orioles experimented with moving Hoyt Wilhelm into a starting role in 1958, which culminated in a nationally televised no-hitter. Bill Lee and Wilbur Wood began their major league careers as relievers; Goose Gossage received a one-year trial as a starter; Rick Aguilera logged 89 career starts. Derek Lowe, of course, made a successful conversion last year, which may have helped assuage any misgivings on the parts of Bowden and Garagiola.

What's interesting about this year's guinea pigs is that Graves and Kim are radically different pitchers. Both were born in the Far East and allow very few home runs; that's where the similarities end. Graves, statistically speaking, is a finesse pitcher--perhaps the most successful finesse closer since the beloved Dan Quisenberry. Kim is a fire-and-brimstone submariner, striking out a quarter of the batters he faces, sometimes at the cost of allowing others too many free passes.

PECOTA has something of a blind spot when it comes to pitchers who switch roles. There's no reliable way to predict ahead of time which reliever might be tested in the rotation; in its effort to be objective, it assumes that Kim and Graves will keep on keeping on in the bullpen. We can, however, use some of PECOTA's approach to evaluate the effect that the transition might have.

By applying a fairly stringent set of criteria, I was able to identify 19 pitchers who made a clean break from relieving to starting. In order to be included in the study, a pitcher needed to have:

  • Made at least 10 starts in year n;
  • Made at least two-thirds of his appearances in year n as a starter;
  • Made at least 40 relief appearances in year n-1;
  • Started no more than three games in year n-1;
  • Pitched primarily as a reliever in years n-2 and n-3;
  • Agreed to appear on Baseball Prospectus Radio.

Graves has been used as a reliever from the earliest moments of his professional career. Kim was a starter in high school and in international competition, but has pitched almost exclusively in relief since coming stateside. Therefore, it's important to select those pitchers who made as neat a break to starting as possible. Wilhelm, who made his transition in the middle of the season, did not make the cut. Nor did pitchers like Jimmy Key or Pedro Martinez, who got their feet wet with a year of relief despite having been groomed as starters. (I'm kidding about the BPR bit, of course, although Will Carroll might well be trying to lock down the Spaceman for a forthcoming appearance as you read this).

In order to evaluate the pitchers, I relied on their baseline runs allowed average (RA) as derived by PECOTA from their three most recent seasons of major league performance. The purpose of the baseline calculation is to remove luck from a forecast line. Gossage posted a 1.84 ERA in 1975, the season before his conversion to the rotation, but did so on the basis of an unsustainably low home run allowed rate while walking a batter every other inning. As the baseline forecast accounts for, he was not likely to sustain that performance going forward, regardless of the role that he fulfilled; it was only after his long year as a starter that Goose learned to be an efficient pitcher, turning his command into a strength as he reeled off a string of nine consecutive dominant seasons. Conversely, Lowe and Scott Garrelts were somewhat better pitchers than their actual RAs would indicate, and their success in their new roles should not have been a huge surprise.

Yes, we're using RA instead of ERA; it's a more reliable predictor, although that's a subject for another article. Everything has been translated to a neutral park and league, using an analogue to the ERA+ convention established by Total Baseball in which 100 indicates a league-average performance and higher scores indicate superior performances.

Table 1: Comparison of Expected and Actual RA+ for relief-to-starter converts

                                      RA+     
Pitcher             Year    Baseline  Actual  Delta
---------------------------------------------------
Turk Farrell        1962    136       126       -10
Gary Bell           1966    119       110       -10
Wilbur Wood         1971    164       175       +11
Tom Timmermann      1972    127       110       -17
Bill Lee            1973    126       150       +25
Rich Gossage        1976    94         96        +2
Doug Bird           1976    112        97       -15
Calvin Schiraldi    1988    94         85        -9
Scott Garrelts      1989    162       148       -14
Greg A. Harris      1990    103       104        +1
Greg L. Harris      1991    131       169       +38
Bill Swift          1992    121       165       +44
Craig Lefferts      1992    94         93        -1
Kenny Rogers        1993    109       100        -9
Rick Aguilera       1996    114       103       -11
Willie Blair        1997    116       116         0
Darren Dreifort     1998    111       103        -8
Hipolito Pichardo   1998    103        91       -12
Derek Lowe          2002    188       181        -7
---------------------------------------------------
MEDIAN                      116       110        -6

The first thing to notice is that, irrespective of the change in roles, a pitcher's previous performance was generally a very good predictor of his future performance. While the majority of the pitchers exhibited a slightly worse RA after making the conversion to starting, the correlation between baseline (predicted) and actual RA+ for our group of pitchers is a remarkably high .83. As we're going to discuss in a moment, there are certain characteristics that are associated with marginal advantages when a pitcher changes roles; that doesn't mean that a great pitcher suddenly becomes a poor one, or the other way around.

But what about those other characteristics? In addition to tracking RA, PECOTA generates baselines for several peripheral statistics, most importantly strikeout rate, walk rate, and home run allowed rate. Like the RA baseline, these metrics are normalized to a neutral league and park. Here are the correlations between those baseline metrics and the difference between predicted and actual RA+ (RA Delta):

Table 2: Correlations between RA Delta and peripheral statistics

        Strikeout rate:   -.46
        Walk rate:        -.20
        Home run rate:    -.39

Heck, even I'm a little bit confused at this point, so let's try a couple of off-speed pitches:

  • The negative correlation on strikeout rate indicates that pitchers who were more reliant on strikeouts tended to fail to perform quite as well as they were expected to after converting from relief pitching to starting. It doesn't mean that strikeout rate isn't important for a starter; a high strikeout rate is still the single best predictor of pitching success. But given the choice between converting pitchers of equal quality, one of whom was a power pitcher and the other was a finesse pitcher, there's some evidence that the finesse pitcher would be more likely to excel in his new role.

  • Pitchers with higher home runs allowed rates tended to make less successful converted starters. Because there was a positive correlation between strikeout rate and home run rate for the pitchers in our sample, it's not clear whether that's indicative of a distinct phenomenon than the effect discussed above. Nevertheless, pitchers who had trouble with the long ball were more likely to see their RA+ deteriorate when they became starters.

To help simplify the analysis, as well as to pay homage to the members of the now-dormant Rob Deer Fan Club, I'd like to introduce a metric known as Three True Outcomes Percentage (TTO%), which tracks the percentage of opposition plate appearances that result in a walk, a strikeout, or a home run. Fortunately, we have a wide variety of TTO percentages within our dataset, ranging from Bill Swift, whose TTO% was a David Eckstein-like 19.9%, to Calvin Schiraldi, who nearly doubled that figure. In the table below, I've sorted our converted starters in order of their TTO%. (Note that TTO% is normalized to the 2002 league environment, in which most every hitter has a bit of Deer blood in him).

Table 3: Pitchers sorted by TTO%

                                     RA+
Pitcher            Year     TTO%   Delta
----------------------------------------
Bill Swift         1992    19.9%     +44
Wilbur Wood        1971    24.8%     +11
Bill Lee           1973    26.0%     +25
Craig Lefferts     1992    26.1%      -1
Tom Timmermann     1972    26.2%     -17
Hipolito Pichardo  1998    27.0%     -12
Derek Lowe         2002    27.6%      -7
Willie Blair       1997    28.1%       0
Rick Aguilera      1996    31.0%     -11
Greg L. Harris     1991    31.5%     +38
Kenny Rogers       1993    31.7%      -9
Greg A. Harris     1990    32.0%      +1
Doug Bird          1976    32.3%     -15
Turk Farrell       1962    32.5%     -10
Gary Bell          1966    33.6%     -10
Darren Dreifort    1998    34.6%      -8
Scott Garrelts     1989    36.9%     -14
Rich Gossage       1976    38.1%      +2
Calvin Schiraldi   1988    39.5%      -9
----------------------------------------
CORRELATION        -.48

The three pitchers with the lowest TTO% all performed much better than expected upon their move to the rotation. Conversely, most of the high-TTO% pitchers performed worse than expected. With a relatively limited sample, it doesn't qualify as categorical proof, but there does seem to be some relationship between the style of pitcher and his likelihood of making a successful conversion to starting. Pitchers who allow the ball to be put into play and let their defense do their work for them tend to do better.

It's always easier to follow statistical evidence with intuition than the other way around, but this result, if it's real, makes plenty of sense. It simply isn't possible to pitch like Calvin Schiraldi for seven innings at a time; the pitch counts rise too quickly, and the strain on the arm is too great. A pitcher like Schiraldi needs to change his approach when pitching for extended stretches in a way that a pitcher like Billy Swift does not. Inevitably, that means allowing a few more runners to reach base. If the pitcher is also vulnerable to the long ball, as Schiraldi was, his RA can rise very quickly as solo shots turn into three-run jobs.

Graves, who has a very low TTO%, and is very efficient with his pitches, is exactly the sort of pitcher who has adapted well in the past to a starting assignment. The news is a mixed bag for Byung Kim. While he's a strikeout-dependent pitcher, he's also become better over time at avoiding home runs and generating groundball outs, which reduces his combustibility if a few extra runners reach base.

The other part of the equation, of course, is how well a pitcher's arm holds up to the increased mileage. Because it's a self-selected collection of players, the group that we've chosen for this analysis doesn't do the question justice. Two of the better statistical comparables for Kim--Garrelts and Darren Dreifort--had Tommy John surgery within a few years of their conversion; whether we have any business comparing a sidearmer with overhand pitchers is another question entirely. Kim has cut down on his pitchers thrown per plate appearance in each of the last three seasons, and he'd be wise to continue to do so as he adapts to his new role. He is likely to be effective so long as his arm stays intact, but his conversion remains a high-risk, high-reward strategy.

Nate Silver is an author of Baseball Prospectus. 
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