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June 12, 1998

The Offensive Explosion That Wasn't

It's an expansion year, so where are the fireworks?

by Greg Spira

Many baseball observers expected an offensive explosion this year as a result of expansion. It has been true in the past that expansion years have coincided with seasons that have featured significant increases in overall offensive levels. These increases have been "explained" as the result of the weak pitching expansion brings into the major leagues.

That explanation has never held up under close scrutiny. Most advocates of the theory either conveniently ignore the minor league hitters that expansion also brings to the majors, or they assume that the talent curve in pitching differs significantly than that in hitting.

When the offensive spikes in expansion years are examined closely, it is clear that expansion pitching is not the primary cause. In the first expansions, in 1961 and 1962, there was no jump in offensive levels. The second round of expansion, in 1969, was accompanied by a large jump in offense, but that was almost certainly caused by the lowering of the mound and the shrinking of the strike zone. The American League expansion of 1977 also accompanied a significant increase in offensive levels, but an increase almost as large was also seen in the National League that year, which did not participate at all in the expansion, not even in the expansion draft. In 1993, when the NL expanded with Colorado and Florida, there was another jump in overall offense. But again the other league experienced a similar jump despite only minor participation in the expansion process (in this case, the draft). (The offensive jump in the NL was greater, but that was entirely the result of the addition of the thin air of Denver to the league.) Also, a look at established pitchers (those who had pitched 100+ innings the previous seasons) saw their ERAs jump as much as the league ERAs did, not exactly what anyone would expect in a year of expansion, and totally inconsistent with any attempt to blame the increase in offensive levels on new expansion.

So there really was no reason to expect an offensive explosion to come along with expansion, but since many believed otherwise, it's worth checking out how much each league is scoring in its established parks compared to previous years.

First, lets look at the National League. We looked at average runs per game in the 14 returning parks in the National League so far this year and compared that to runs per game overall in the National League during the two previous seasons.

1996 9.37
1997 9.21
1998 9.14 (data through games of June 8)

Obviously, we'll have to wait for that offensive explosion in the NL. The slight decrease in runs over the last few years could easily be explained by random fluctuation, though the introduction of Turner Park and national weather patterns could also be influences.

As far as the American League goes:

1996: 10.77
1997: 9.86
1998: 10.21 (data through games of June 8)

While offense has increased somewhat from last season, it has not neared the level of 1996. Note that County Stadium, which was not included in calculating 1998 National League figures, is included in 1996 and 1997 AL calculations, but that in those years the park appeared to be pretty neutral anyway. Tropicana Field appears to be an extreme hitters park, to the surprise of many, increasing AL run scoring somewhat significantly beyond what the 1998 figure above (which does not count runs scored there) shows.

In conclusion, this season's lack of a significant increase in offensive levels suggests that the supposition that expansion cause higher offensive levels because of the addition of expansion pitchers is indeed wrong, as earlier studies have suggested. Expansion almost certainly does produce at least a temporary drop in quality and therefore an increase in how many players perform highly above or below the mean, but that does not result in a significant change in the mean itself.

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1998-09-15 - A Quick and Dirty Guide to 1998 Park Factors
1998-08-28 - BP Polling: Greg Spira's Ballot
1998-06-12 - The Offensive Explosion That Wasn't
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