Kauffman Park Effects

An email from Ron Hostetter inquired about the ballpark effect of Kauffman stadium because of a quote he saw in book on ballparks published in 1998. In essence the comment said: "The change from artificial turf to grass has changed baseball in this park. It is now a pitchers’ park. The number of hits, doubles and triples have been reduced significantly. Although the fences down the line and in the power alleys were brought in 10 feet in 1995, homering at the park remains more difficult than at a neutral park (about 15 percent more difficult). "

However, the last few seasons have seen the K act as a boon for hitters increasing run production by 30% for a ballpark factor of 130 as calculated in The Bill James Handbook 2004. I went back and pulled the numbers from baseball-reference.com and found the following;

	Home				Away			Index		

	Games	Royals	Opp	Opp%+	Games	Royals	Opp	Opp%+	Royals	Opp	Overall

2003	80	433	512	18%	82	403	355	-12%	10%	48%	28%

2002	81	434	505	16%	81	303	386	27%	43%	31%	36%

2001	81	382	485	27%	81	347	373	7%	10%	30%	20%

2000	81	451	488	8%	81	428	442	3%	5%	10%	8%

1999	80	441	449	2%	81	415	472	14%	8%	-4%	2%

1998	80	353	492	39%	81	461	407	-12%	-22%	22%	-1%

1997	80	387	434	12%	81	360	386	7%	9%	14%	11%

1996	80	372	369	-1%	81	374	417	11%	1%	-10%	-5%

1995	72	285	346	21%	72	344	345	0%	-17%	0%	-8%

1994	59	325	287	-12%	58	249	245	-2%	28%	15%	22%

1993	81	370	354	-4%	81	305	340	11%	21%	4%	12%

1992	81	314	346	10%	81	296	331	12%	6%	5%	5%

1991	81	344	378	10%	81	383	344	-10%	-10%	10%	-1%

											

91-94	302	1353	1365	1%	301	1233	1260	2%	9%	8%	9%

95-03	715	3538	4080	15%	721	3435	3583	4%	4%	15%	9%

Note: These stats include interleague games.

From the above chart it is interesting to note that in the 1991-1994 period (supposedly when the hitters had the advantage) the ballpark produced 9% more runs (a ballpark factor of 109) while from 1995-2003 when changes made it more amenable to pitchers it was also 109. For some reason the 1995 and 1996 numbers were much lower than in almost all the other years. One possible explanation is that weather patterns in Kansas City changed over the last few years producing hotter, sunnier, and breezier days than previously and so even though the changes in the 1994 offseason made the park more of a pitcher's park, the weather more than compensated in the last few years. Another possible explanation is that the data is too variable to say definitively how much of an advantage or disadvantage hitters have at the K. The standard deviation when all years are taken into consideration is .15 which seems pretty big to me.

Perhaps the bigger question is why in 7 of the last 9 years the Royals opponents have scored so many more runs proportionately at the K than the Royals have? The opponent's huge numbers at the K scoring 15% more run while the Royals score only 4% more have inflated the park factor. So why is it that the Royals seem to give up so many runs at home? Email me if you have any ideas.