MLB American League Domes Have No Influence on Foul Ball Rates 1988-1996 Data Indicates

It’s been slow going, but I’ve finally gotten through the foul ball count for the American League from 1988-1996. Interestingly, few patterns showing up anywhere. One of those patterns has to do with the Toronto Blue Jays. Notice in the chart below, that the Blue Jays consistently have the highest total of foul balls hit during home games. Consistently.

My working theory on this consistently higher average total is that they are one of three teams that played in a domed stadium (Twins, Blue Jays and Mariners) during this nine year period. In a dome, there would be less wind resistance, so balls wouldn’t be effected by sudden gusts of wind, or not go as far as a result of humidity. Essentially, weather factors associated with outside play are nearly all nullified. The only environmental effects on the ball would be any breeze from the air conditioning and the temperature in the dome.

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However, when we look at the data, the consistently high rate of foul balls at Blue Jays home games, doesn’t transfer to the Twins and Mariners.

Legend: Red: Highest total for season; Blue: Lowest total for season; Orange: 1994 and 1995 were shorter seasons due to strike Green: Year strike zone was increased.
Legend: Red: Highest total for season; Blue: Lowest total for season; Orange: 1994 and 1995 were shorter seasons due to strike
Green: Year strike zone was increased.

 

The Seattle Mariners played in the Kingdome during the same time period, yet their foul ball counts are significantly lower. But here’s the thing about the Mariners. The team’s numbers are the most consistent of all the teams during this timeframe. The data shows that the Mariners are consistently the lowest of the three teams. They also have the second lowest overall average through the nine season period. The Mariners rates up until the season shortening strike has a deviation of only one foul ball between highest and lowest season totals.

 

The Twins, on the other hand, are essentially at the league average for this timeframe. As a result, there doesn’t seem to be any consistency with respect to how a dome might influence foul balls. What this is telling us is that playing in a dome has no consistent effect on hitting. The data shows the full spectrum. They also have a wider deviation over the years.

 

There is only one way to determine if this theory is valid, that domes have a noticeable influence on foul ball rates due to the removal of environmental interference, is to finish all the years and see if this is an actual pattern.

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Given the Mariners were so consistent, the Twins were on par with the league average, and the Blue Jays had the most fouls 6 of the 9 years covered so far, were in second place one year, third another season, and the lowest one other year, it appears domes don’t have a consistent effect on foul ball rates. But only more data will tell us for sure.

 

Note: All data is from retrosheet.org sources. Some teams are incomplete, so foul ball rates will be marginally inaccurate. Based on missing data, I estimate a +/-2 foul ball range if all statistics were available.