Park Factor at SkyDome

In a post last week, I said the following:

Skydome (well the Rogers Center) does seem like it's a fairly hitter-friendly park (in the early 2000s, it's "Park Factor" was over 100 consistently, which means it favored hitters, while in the last couple of years it has been below 100 a couple of times).

I have thought about the statement a lot, and decided to do some more research on the topic, as I do not like making statements without valid statistical analysis backing me up.

You can read all about ballpark adjustments and factors here. That post will show you how to calculate the ballpark factor for a park over one year or multiple years, but since the statistics have already been calculated and are already on the corresponding team and year page, you can take them from there. The numbers will all be around 100, as 100 represents a "medium" ballpark, with no advantages to batters or pitchers. If the number is above 100, the ballpark favors batters, and if it is below 100, it favors pitchers.

I have taken statistics from each year for the Blue Jays since 1990. The SkyDome opened midway through 1989, and since the statistics will be skewed for that year I decided not to include it, but since then the Jays have played all of their home games at the SkyDome. I took the ballpark factor for both multi-year and one year, the number of home runs and number of extra base hits at the SkyDome and away each year (81 games, except for 1994 and 1995 because of the strike, and 2010, which is projected), and finally the batting average and batting average on balls in play for the Jays at home and away. I have constructed a couple of graphs which I believe show that the SkyDome is in fact a fairly friendly hitter's park. (Click on any graph to enlarge it and see more detail.)

The first graph is all home statistics. I wanted to compare the park factor to the number of home runs the Jays hit at home each year. As we can see by the trendlines, the park factor and number of home runs have no correlation at all, as the park factor has stayed fairly constant (actually decreasing by about 0.2 per year), while the home runs have varied widely, with an average gain of 1.3 more home runs per year. This graph shows that the park factor calculations take into account a lot more than just home run totals.

Now I am going to look at home and away splits. Each of the following graphs shows a different statistic presented in home vs away fashion, and the goal is to get a visual representation of whether or not the SkyDome is in fact a hitter's park. Although on average, teams should hit better at home than on the road (familiarity of the stadium and its intricacies, fans cheering instead of booing, the comfort of home, etc.), the actual increase is hard to quantify, and thus, we must assume that home and away statistics should be even. We are also assuming that the road statistics are based on an average ballpark factor of 100, because we are trying to compare home vs away statistics, we want to determine the "friendliness" of the SkyDome to batters.

The first graph shows the number of home runs hit by the Blue Jays at home and on the road each season from 1990 to 2010. This graph is a pretty clear indication that the Jays hit a lot more home runs at home than on the road, especially in the last decade or so. The trendlines show that approximately 1.3 more home runs are hit at home per year, while only about 0.5 more home runs are hit on the road per year. So, we can say with good certainty that the SkyDome is more home run friendly than the average American League ballpark (since the large majority of their away games were played in the AL).

The next graph will compare the extra base hits at home and on the road. Although we already looked at home runs, it is important to look at extra base hits because we want to determine whether the balls that are not home runs on the road will either fall in the gaps for doubles or triples or whether they will be caught. If they find gaps, then the away stadium is still mostly hitter friendly, but if the balls that usually leave the park at home get caught on the road, then we know for sure that the SkyDome is much more hitter friendly for power statistics. We can see from the graphs that almost every year there are more extra base hits at home than on the road, other than a couple of isolated years in the 90s. So since there are more home runs and just as many extra base hits at home, we can safely say that the SkyDome is an above-average hitter friendly park.

The last thing I want to look at is the batting average splits. We have seen that the SkyDome is hitter friendly for power, but we also want to find out if it is hitter friendly for average. I chose to look at both batting average and batting average on balls in play, since batting average can be very inconsistent (although team batting statistics for 81 games is a fairly large sample size). Although the trendlines are almost constant in all of the cases below, we can take the average average for each statistic from them. The average batting average at home is 0.267, and on the road it is 0.264. For BABIP, at home the average is 0.297, while on the road it is 0.294. Although these are only small differences, over the course of 21 years they can become significant changes. Although we may not be able to say that hitting for average at the SkyDome is easier than on the road (see the above explanation for why hitting at home may be easier), we can say that it is at least just as easy at home as on the road.

So after taking a look at the home vs away splits for the last 21 years, I am confident that what I said last week is true. I am glad that my analysis shows that what I said was true, and that I wasn't just saying false facts. SkyDome is in fact a hitter friendly park in comparison to other American League parks, both for power and somewhat for average.