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Friday, May 02, 2008
What do good and bad starts by pitchers tell us?
I looked at the first month of the season (April only) ERA for all pitchers who were either exclusive relievers or exclusive starters. I did this for 04-07.
From these, I put them into two groups: Those that started out great in ERA and those that started out terribly.
For starters, I used an ERA of over 6 or under 3 for a poor or great start. For relievers, I used 5.2 and 1.8. This created 82 and 89 pitchers in the two starter groups, bad and good starts, and 68 and 91 pitches in the two reliever groups. Again, that is for 4 years combined. There might be duplicate pitchers (probably are) in some groups from year to year. Not in the same year of course.
For each pitcher in each group, I computed his projected ERA before the season started, using a crude Marcel with no age adjustments (I did do a regression).
I also computed their projected ERA after the one month of great or poor performance, updating the pre-season projection with the new information by weighting the new information twice the amount of the prior (pre-season) information. Finally, I looked at their ERA for the remainder of the season.
Here are the results and some commentary:
IP1 is the number of IP in April
ERA1 is the ERA in April
preERA1 is projected ERA before season started
preERA2 is the projection updated after April was over
ERA2 is the ERA for the rest of the season (AFTER April)
Starters
Bad start
N age IP1 ERA1 prERA1 prERA2 ERA2
82 31.2 27 7.12 4.43 4.56 109 4.70
Starters
Good start
N age IP1 ERA1 prERA1 prERA2 ERA2
89 31.7 33 2.25 4.15 4.05 152 4.09
I’ll make a couple of comments here. I am guessing that the ones who started out real bad were more injured as a group, and that is why they were .14 runs worse than their updated projection, although .14 runs is not a whole lot to get excited about. Also, I did not do any age adjustments in my Marcel projections, so since these pitchers averaged in their early 30’s (31.7) a little worse than their projection is probably expected for all groups.
Anyway, the starters who started out great essentially pitched at their projected level - in fact, a little worse (not statistically significantly worse, I am assuming). So, at least with regard to these guys AS A WHOLE, PLEASE don’t try to tell me who is “real” and who is not. Everyone pitches to around their expected level.
Now the relievers. Obviously, they don’t average many innings in one month, but we still see a lot of talk about them, like Turnbow is no good anymore, etc.
Relievers
Bad start
N age IP1 ERA1 prERA1 prERA2 ERA2
68 32.1 12 6.78 4.12 4.22 47 4.12
These guys actually pitched better than their updated projection, although, again, I doubt that the difference is statistically significant. But it looks like there is nothing going on when relievers pitch badly in the first month of the season. And we are only talking about 12 IP each.
Relievers
Good start
N age IP1 ERA1 prERA1 prERA2 ERA2
91 32.5 12 .92 3.95 3.84 54 3.68
These guys who pitched great for 12 IP in April exceeded their updated projection by .16 runs, which is good, but again, nothing to write home about, and also probably not statistically significant.
Let’s look at some other subsets of players just for fun:
Here are young pitchers only - less than 27 years old. There are not a whole lot as you could guess from the average age of the entire group above. Beware of sample size issues here.
Starters
Bad start
N age IP1 ERA1 prERA1 prERA2 ERA2
8 25.0 26 6.63 4.72 4.83 94 4.74
Nothing unusual here. If you are young and you start out real badly, it doesn’t seem to mean much. Your projection is your projection. They actually pitch a little better than expected, but that might be an aging thing again.
Let’s look at the young guns. The young starters who started out lights out.
Starters
Good start
N age IP1 ERA1 prERA1 prERA2 ERA2
12 25.3 32 1.95 4.31 4.11 149 3.60
Wow, they exceeded their projection by .51 runs. We are only talking about a total of 1783 IP, but that is still quite impressive. Even if we assumed a .1 or .2 decrease due to aging, they still exceeded that.
The young relievers show nothing remarkable, so I won’t even show their stats, plus we really have small sample sizes for them.
How about the old guys (33 and over)?
Starters
Bad start
N age IP1 ERA1 prERA1 prERA2 ERA2
26 35.9 25 7.25 4.38 4.47 108 4.82
Maybe when an older pitcher pitchers badly, it is a suggestion that he is near the end. Or again, maybe it is just because I am not doing any aging adjustments plus the injury thing, and that these guys really need to be age adjusted aggressively.
Starters
Good start
N age IP1 ERA1 prERA1 prERA2 ERA2
29 38.2 33 2.34 4.05 3.99 144 4.31
Hmmm. They also pitch a lot worse than expected. It is probably the lack of aging adjustments again. If we tack on another .3 in ERA or so for both the good and bad April pitchers, for these old guys, for aging, they pitch about what they are expected to pitch. So really nothing remarkable there. For example, unless there is something specific about Morris’ pitches, independent of his performance thus far (which is why you CANNOT let your scouts see numbers, although you can’t avoid it with MLB pitchers of course), I just don’t see how you can write him off after one month. What gives you the right to do that? According to this model, I had Morris with a projected normalized (to 4.50) ERA of 4.65 going into the season. Even if you add .5 runs for aging and his bad start, he is still better than replacement level. Teams and fans will always, always, always (did I say always?) overvalue recent performance, good or bad.
Finally, and again, just for fun, let’s look at pitchers, like Cliff Lee, who are not too old or young, and look like they have finally turned the corner. These are the guys who did not have a great projection going into the season, but have pitched lights out for the entire month of April. These are the guys that hundreds of articles are written about, right? Are they for real?
I am restricting to ages 27-31 and those starters who had a pre-season projection of greater than 4.25:
Starters
Good start
N age IP1 ERA1 prERA1 prERA2 ERA2
20 28.9 32 2.22 4.55 4.38 147 4.19
Well, they definitely did better than expected, but not quite the studs they looked like in April. I will grant them a (very) partial “for real” on the order of .25 runs or so (the .19 above plus a little for aging), which is not wood. That was not the case for relievers, BTW.
Finally, how about the not so young or old starters who were supposed to be good, but really stunk in April? Was their projection just a mirage?
Starters
Bad start
N age IP1 ERA1 prERA1 prERA2 ERA2
5 29.4 28 6.92 3.80 3.99 123 3.86
There were only 5 pitchers, so sample size beware, but they appeared to do just fine if left alone. The 16 relievers to make this list did the same. They pitched at a 7.18 ERA clip in April, but 3.77 the rest of the season (with a projection of 3.97).