Doctoring the Numbers: Offense in Colorado

by Rany Jazayerli

This year marks the tenth season of major league baseball in Denver. It is clear now that none of us fully understood what we were getting ourselves into when we allowed Rocky Mountain thin air to be unleashed on our national pastime. Nine years and literally thousands of hanging curveballs, home runs, and destroyed pitcher psyches later, we're still trying to wrap our hands around the conundrum that is baseball at altitude.

(And before you mention the word "humidor", consider that with the recent run of explosive offense at Coors Field, the Rockies and their opponents have combined to score 11.74 runs per home game, compared to 8.61 runs per game on the road - a 36% increase. It may no longer be the best hitters' park of all-time - Coors Field increased run scoring by 58% from 1999 to 2001 - but it's still the best hitters' park of our generation.)

Don't get me wrong: 5,280 feet has been an enormous blessing for baseball, providing us all with a unique and pyrotechnic-rich setting for the game. Coors Field is a tremendous asset for the major leagues; it is also a tremendous burden for the Colorado Rockies, who have failed for years - and not for a lack of effort - to come up with a philosophy that will work in their home ballpark. They've tried bringing in free-agent hitters and drafting pitchers; they've thrown a fifth of a billion dollars at free-agent pitchers. They've tried to cram the lineup with mashers; they've tried to man their outfield with speedsters to haul down every fly ball. So far, nothing has worked.

Some of my colleagues feel that they've come up with the answer, or at least an answer. As Joe Sheehan wrote in the Rockies' chapter of Baseball Prospectus 2002:

"Hitting" is the key element at Coors Field. The worst thing you can do is strike out, because the outcome of putting a bat on the ball is better there than it is anywhere else. Players hitting in Coors Field batted .312 last season, with a .535 slugging percentage. When they didn't strike out, though, those numbers jumped to .378 and .649. Think about that: simply not striking out makes you a .380 hitter with great power at Coors Field.

Joe continues:

The Rockies should therefore choose players who put the ball in play, all else being equal, and they should encourage approaches at the plate that reduce strikeouts without having a detrimental affect on OBP. Todd Helton and Larry Walker are going to help a team no matter what, but on the margins, it's better for the Rockies to have a player who strikes out 50 times rather than 80, even if there's a slight loss in expected walks. The extra balls in play will help them win games at home. Someone like Juan Pierre, with 41 walks and 29 strikeouts in 600-odd at-bats, really is a worthwhile player in Coors Field.

The theory makes a good deal of sense, and is slowly gaining acceptance in baseball circles. There's only one problem with it: in my opinion, it's 100% incorrect.

Let's backtrack for a moment here. The central point to this theory is that a ball put in play is much more dangerous in Coors Field than elsewhere. But is it really? The National League as a whole hit .261 with a .425 SLG in 2001; with strikeouts removed from the equation, they hit .328 with a .534 slugging average. Let's put that in chart form: 

                  Overall         Contact    Ball in Play

Coors Field     .310/.534       .376/.647       .338/.447
NL              .261/.425       .328/.534       .299/.382
Difference    +.049/+.109     +.048/+.113     +.039/+.065

"Ball in play" refers to balls that the defense can reach, i.e. home runs are taken out of the equation. The first number shown is batting average, followed by slugging average.

The first thing to note is that my numbers for Coors Field are a few percentage points off from Joe's numbers. Joe looked at only the Rockies non-interleague games, while I looked at all of their games, in order to fairly compare their numbers to the NL as a whole. The difference is trivial, regardless.

Certainly, the performance of hitters at Coors Field when they don't strike out looks awfully impressive. But compared to the league as a whole, Coors Field hitters only hit 48 points and slugged 113 points higher when they made contact. Compare that to how the hitters did in all situations - Coors Field increased offense by 49 points of batting and 109 points of slugging, virtually identical totals.

So the difference isn't simply that hitters are much more likely to get a hit when they make contact. The difference is that hitters are much more likely to make contact. Coors Field cut strikeouts (as a percentage of at-bats) by roughly 14% from 1999 to 2001. (Interestingly, so far this year Coors Field has only cut strikeouts by 9%, suggesting that the humidor isn't only making the balls less bouncy, but the increased humidity of the balls may be helping pitchers get a better grip on the seams, allowing their breaking pitches to curve better.)

That's not to say that balls in play aren't more difficult to field at altitude. As the above chart shows, even when homers are removed from the equation, hitters bat 39 points higher on balls in play, and a slugging average increase of 65 points suggests that doubles and triples are more common as well.

Breaking it down into its component parts, then, we can more accurately say that Coors Field:

  1. decreases strikeouts by about 14% (pre-humidor);
  2. increases home runs by about 60%;
  3. increases batting average on balls in play by about 49 points.

The last point can also be looked at from the point of the defense, since batting average on balls in play is simply the inverse of Defensive Efficiency. Defensive Efficiency is decreased by about 39 points at Coors Field.

Let's apply this to what Joe's last sentence: "Someone like Juan Pierre, with 41 walks and 29 strikeouts in 600-odd at-bats, really is a worthwhile player in Coors Field."

Juan Pierre:

  1. rarely strikes out, so he gets little benefit from the reduction in Ks at Coors Field;
  2. never hits homers;
  3. puts the ball in play nearly 90% of the time.

While Pierre benefits from (3), he gets less benefit from (1) or (2) than just about anyone in the game. This is your model for a Coors Field hitter?

The proof is in the pudding: Pierre has a career .333 batting average and .392 slugging average at Coors Field. On the road, his career numbers are .280 and .341. He has picked up an additional 53 points of batting average from his home ballpark, a smidge higher than the 49 points a typical player picks up (but keep in mind, the typical player hits a few points better in his home park regardless). But because he has no power to speak of, the bump in his slugging average is less than half that of the typical ballplayer (51 points vs. 109).

Juan Pierre is not the ideal Coors hitter. On the contrary, he's close to the antithesis of one.

Walt Weiss, another punch-and-judy hitter who rarely struck out, spent four seasons at Coors Field, and in that time he hit 63 points better - but with a slugging average just 72 points higher - at home.

What is the ideal Coors hitter? Simple: someone with power. Look back at the list of how Coors Field influences offense. Points (1) and (3) essentially cancel each other out, because good contact hitters will benefit from the positive effects on balls in play, but poor contact hitters will benefit from the decrease in their strikeout totals.

Want proof? Let's describe two theoretical hitters, one of who strikes out in 30% of his at-bats (corresponding to 180 Ks per 600 at-bat) - we'll call him Rob Deer - and another who strikes out in 5% of his at-bats (or 30 K's per 600 at-bats) - let's name him Tony Gwynn. This is a rough representation of the two extremes among hitters today.

Let's assume that Deer and Gwynn both bat 300 times at Coors Field, and 300 times in a sea-level environment. In Colorado, Deer is going to see his 90 strikeouts on the road drop by 15%, to 76.5, putting 13.5 more balls in play. Overall, though, he will only make fair contact with 223.5 pitches. Gwynn, on the other hand, will see his strikeouts drop marginally, from 15 on the road to 12.25, but he'll take advantage of Coors' friendly effects on batted balls 287.25 times.

At sea level, Deer will make contact with 210 pitches, and since the average hitter bats .328 when he makes contact at sea level, he would be expected to hit safely 68.9 times. In Colorado, he makes contact 223.5 times, and bats .376 when he makes contact; that's 84.0 hits.

At sea level, Gwynn would put 285 balls in play, and would expect to garner 93.5 hits. At Coors, that's 287.25 balls in play, and 108.0 hits.

So Deer's hit total at home would increase by (84.0 - 68.9 =) 15.1 hits. Gwynn would pick up an extra (108.0 - 93.5 =) 14.5 hits.

In other words, the strikeout-prone Rob Deer benefits more from Coors Field than his contact-minded teammate. Granted, the difference is marginal - about half a hit per season - but clearly, there is no benefit to having players whose primary skill is putting the ball in play.

That leaves point (2), which is that homers go up about 60%. The more power you have in your lineup, the more additional power you'll pick up from Coors Field. Period.

At another point in the article, Joe writes, "The extra boost given to batted balls also made walks relatively less valuable. The positive expectation of a ball in play - .378 OBP, .649 slugging - takes away much of the incentive to work deep counts, because deep counts increase the odds of a costly strikeout. Given the decreased value of walks in Coors, the aggressive approach of Vinny Castilla and Dante Bichette - the greatest beneficiaries of Coorsflation - almost makes sense."

Hold it right there. "The extra boost given to batted balls also made walks relatively less valuable" - that goes against everything I've grown to understand about offense. Earl Weaver never claimed his success was predicated on "pitching, defense, and solo homers", and not for a minute do I think he would have made that statement if he had spent his whole career at Coors Field. If there's one thing we understand about the nature of offense, it's that there's a synergistic relationship between the ability to get on base and the ability to drive in runners. To say that walks are less valuable because the next hitter is more likely to drive you in with an extra-base hit - I don't get it.

Look at the opposite situation - a great pitching environment, like Dodger Stadium in the 1960s or the Astrodome. When runs are at a premium and batters are much less likely to get a base-hit, a walk isn't nearly as valuable, because it's less likely you're going to be driven in from first base. Outs also become less precious as one-run strategies like bunting and stealing make more sense from a strategic standpoint, because when you're less likely to score, trading outs for an increased chance at one run makes sense. And if outs are less precious, then avoiding outs (by getting on base) becomes a lesser priority.

In Coors Field, on the other hand, where you can put up crooked numbers at any time, you never want to give up an out - so why would the ability to get on base (and avoid outs) be less valuable? And if getting on base isn't less valuable, then how can the ability to draw a walk be less valuable?

I think Joe's point was not so much that walks are bad, but that the by-product of better plate discipline is frequently more strikeouts. That's not always the case, but even if it is true, since we've already established that you're less likely to strike out in Coors Field, it makes the tradeoff even more appealing.

Regarding the second point--Castilla and Bichette certainly did benefit more from Coors Field than, say, Pierre and Weiss. But that's in large part because of the increase in the home run totals, not because they put more balls in play than the average hitter. In five years at Coors Field, Bichette hit 110 homers at home, just 43 on the road--that's an additional 14 homers a year, enough to raise his batting average at home by nearly 50 points by itself. During the same time span Castilla hit 117 homers at Coors, 74 homers elsewhere. That is why they did so well at Coors Field--because they nearly doubled their home run output at home.

Do we have any proof that a hitter with high strikeout totals can thrive at Coors Field? Of course - consider Andres Galarraga, who as a member of the Expos led the NL in strikeouts three straight years, from 1988 to 1990. In his first season at altitude, all he did was win a batting title, in large part because his strikeouts dropped precipitously; after average a strikeout in 25.2% of his at-bats previously, the year he hit .370 he struck out only 73 times all year, or in just 15.5% of his at-bats. During his five years with the Rockies, Galarraga struck out in 26% of his road at-bats, but just 19.8% of his at-bats at home - a reduction of 24%.

Next week, I'll break down how Coors Field impacts pitching and defense, and what the Rockies' optimum strategies are when they take the field.

Rany Jazayerli is an author of Baseball Prospectus. You can contact him by clicking here.

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