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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.