Scott Lewis and Cold Weather

by ClarkM on Mar 21, 2009 2:14 PM EDT

The battle for the fifth spot in the rotation continues, and there may be a new favorite. Scott Lewis has followed up an impressive cup of coffee in September with a fine showing in Spring Training. Aaron Laffey and Jeremy Sowers are still in the mix, but Wedge’s comments seemed to me and Castrovince that Lewis might get the first shot at the rotation.

First shot at the rotation should be emphasized because Laffey and Sowers (and Huff and Jackson) are going to get their shots. Somebody is going to get hurt and/or someone is going to be ineffective so ultimately it may not matter a whole lot who wins the job out of the gate. With that being said, there may be real reasons, other than overall qulaity, to prioritize one guy over the other. Anthony Reyes, for example, is starting in the rotation because he’s out of options.

In Scott Lewis’s case, it might not be more than a case of riding the hot hand, but I think there might be another reason. Lewis is a fly-ball pitcher, a 39.3 career GB% in the minors. The average GB% amongst starting pitchers in the majors last year was 43.45%. This may be significant because conventional wisdom is that the ball doesn’t carry as well at beginning of the season, when the weather is cold. If this is true, Lewis would be benefited by this much more than Laffey.

To see if the conventional wisdom is in fact correct, I looked at some basic numbers. Thanks to Baseball-reference.com, I computed home runs per plate appearance in each month over the past five years in the American League. The lower the number, the more frequent the home runs.

Year/Month	2004	2005	2006	2007	2008
April	37.45	40.09	32.25	38.97	43.82
May	35.79	36.93	34.79	36.58	44.16
June	34.32	33.97	34.22	41.03	35.02
July	31.67	33.84	33.63	40.85	36.22
August	30.88	33.94	35.77	38.61	35.83
September	34.81	36.6	35.81	38.43	38.36

This is obviously a very crude way to look at it and I don’t think it really tells us that much, but three of the five seasons do seem to support the cw, for whatever that’s worth. Even if it is true that fly balls don’t carry as well at the beginning of the season, the overall effect is probably not that great. But given that the difference in quality between the pitchers is small, this could potentially be a tie-breaker. Looking over the schedule, the fifth starter is set-up to get, at least his first few starts in cold weather open-air stadiums.

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Interesting. I have to think about this.

by afh4 on Mar 21, 2009 2:33 PM EDT reply actions

Here’s an article from THT about cold weather affecting the 2006 post-season (OCT weather).
The author goes about the same assumptions but doesn’t really provide evidence to support those assumptions.

This article I found was interesting, as the author claims to be a teacher of Astronomy and a former meteorologist. He says humidity has a marked impact on drag:

Without going into a whole lot of technical jargon, if you add water to
dry air, it will vaporize and since water vapor has less density than dry
air, the ball should be helped along in its flight. Therefore, high
humidity creates longer flights and hopefully more home runs.
Unfortunately, if the humidity gets high enough where fog, mist, or rain
may occur, the droplets of moisture will lead to a high density of the
air, increasing the aerodynamic drag, and therefore reducing the distance
the ball will travel

and here again the assumption that the ball travels farther in warm weather:

Now the temperature comes into play. The warmer the temperature, the
farther the ball will travel. At 65 degrees, that 400 foot fly ball would
actually travel 408 feet, at 85 degrees, 416 feet, and at 95 degrees, 420
feet. All of this assumes no wind. A ten mile an hour wind towards the
batter will decrease the flight to 370 feet, while a wind away from the
batter will increase the flight to 430 feet. Then we have to take into
account the atmospheric pressure. A dropping of pressure of only an inch,
will add about five feet of flight to the ball. And according to the laws
of physics, the farthest a ball can be hit, at sea level, under perfect
conditions, is 545 feet!

Here’s a link that references The Physics of Baseball by Robert K. Adair.

A colder ball will have a lower coefficient of restitution (COR) (bounce/spring/elasticity) which is a measure of its ability to retain kinetic energy after a collision. A lower coefficient of restitution will result in more energy loss at contact, and therefore less distance travelled by a batted ball. Conversely, a warmer ball will have a higher COR. Adair reports that a batted ball that would go 375 feet at 70 oF will travel 3 feet farther for every 10oF increase in temperature and will travel 3 feet less for every 10oF drop in temperature. Remember this the ball’s temperature. It will take some time for the ball to achieve ambient temperature.

He also notes that the cold weather effects the bat as well, so the dampening effect should be considered not only on the ball thrown but the bat swung.

What would be interesting if this is in fact one of the reasons for going with Lewis over Laffey or Sowers (although Sowers isn’t necessarily a groundball pitcher either) would be how they handle Lewis once the weather warms up, is he simply given a shorter leash than another starter because of the assumed effect of warmer weather on his allowed fly balls?

by hans on Mar 21, 2009 4:30 PM EDT reply actions

~~Sowers~~

Don't be stupid. PUT IN MELOAN.

by gte619n on Mar 22, 2009 11:20 AM EDT up reply actions

In Sower’s major league career, he has been almost exactly average at inducing groundballs, so he’s not really a groundball pitcher or a flyball pitcher. For his minor league career, the larger sample, he’s been close to 50%.

This brings up an interesting question, how do groundballs translate from level to level? Generally, strikeout rates go down as the competition gets better and walk rates go up, but what about groundballs? Since groundballs are a desired result for pitchers, it might make sense to think that they are harder to induce as the competition gets tougher, but for some reason, I don’t think that’s the case.

by ClarkM on Mar 22, 2009 11:41 AM EDT up reply actions

I couldn’t find anything, but admittedly only looked briefly, discussing groundball rates from the minors compared to majors. My assumption is that the control lies with the pitcher and that the majority of hitters do not have the ability to elevate hard sinkers on a regular basis, so basically if the pitcher can maintain accuracy and velocity on the sinking fastball then even major league hitters will pound the ball into the ground more often.

by hans on Mar 22, 2009 2:44 PM EDT up reply actions

Here’s the thing: Although the cold weather makes Lewis a better pitcher in theory, it doesn’t make Laffey a worse one. It makes him better too, because every pitcher (yes, even Jake) gives up some fly balls.

So Laffey becomes worse, only as a percentage relative to Lewis’ increased effectiveness over his.

Travis Hafner is overrated. Clarity is underrated. David Dellucci is David Dellucci.

by westbrook on Mar 21, 2009 5:23 PM EDT reply actions

Yeah, I thought that is what I said.

by ClarkM on Mar 22, 2009 1:04 AM EDT up reply actions

Yeah, I think you nailed the Lewis half of it. I just wanted to add a little about Laffey, which happens to also apply to Reyes, Sowers, Huff and Jackson.

Travis Hafner is overrated. Clarity is underrated. David Dellucci is David Dellucci.

by westbrook on Mar 22, 2009 2:25 AM EDT up reply actions