R=HR/(AB-K)
Before doing this, my belief was that Coors field would not ave the highest rate. I also had a suspicion that a certain stadium would have the highest rate. So I ran the numbers, looking at both the home team's and away teams' home run rate for each stadium in 2009. Here are the results:
| Club | Stadium | Team | Opponents | Total |
| NYY | Yankee Stadium III | 5.96% | 4.61% | 5.30% |
| TEX | Rangers Ballpark in Arlington | 5.80% | 4.02% | 4.87% |
| PHI | Citizens Bank Park | 5.02% | 4.42% | 4.71% |
| MIL | Miller Park | 4.83% | 4.55% | 4.69% |
| CHA | Comiskey Park II | 4.77% | 4.03% | 4.40% |
| TOR | SkyDome | 4.67% | 4.07% | 4.37% |
| CIN | Great American Ballpark | 4.46% | 4.20% | 4.33% |
| TAM | Tropicana Field | 4.97% | 3.70% | 4.31% |
| BOS | Fenway Park | 5.38% | 3.26% | 4.30% |
| BAL | Oriole Park at Camden Yards | 4.15% | 4.42% | 4.29% |
| LAA | Angel Stadium of Anaheim | 4.01% | 4.53% | 4.27% |
| DET | Comerica Park | 4.26% | 3.98% | 4.12% |
| MIN | Hubert H. Humphrey Metrodome | 4.22% | 3.87% | 4.04% |
| ARI | Chase Field | 4.07% | 3.82% | 3.94% |
| COL | Coors Field | 4.59% | 3.30% | 3.93% |
| FLA | Dolphin Stadium | 3.99% | 3.74% | 3.87% |
| MLB Average | 4.00% | 3.63% | 3.81% | |
| CHN | Wrigley Field | 3.87% | 3.74% | 3.80% |
| HOU | Minute Maid Park | 3.57% | 3.84% | 3.71% |
| WAS | Nationals Park | 3.57% | 3.57% | 3.57% |
| SEA | Safeco Field | 3.50% | 3.51% | 3.51% |
| OAK | Network Associates Coliseum | 3.25% | 3.07% | 3.16% |
| PIT | PNC Park | 3.39% | 2.92% | 3.15% |
| SDG | PetCo Park | 3.05% | 3.16% | 3.11% |
| SFG | AT&T Park | 3.11% | 3.07% | 3.09% |
| CLE | Jacobs Field | 3.10% | 3.05% | 3.07% |
| KAN | Kauffman Stadium | 2.87% | 3.01% | 2.94% |
| LAD | Dodger Stadium | 3.18% | 2.68% | 2.94% |
| NYM | Citi Field | 2.22% | 3.61% | 2.92% |
| ATL | Turner Field | 3.18% | 2.55% | 2.87% |
| STL | Busch Stadium II | 3.06% | 2.41% | 2.73% |
As you can see, the new Yankee Stadium comes out on top, with 5.3% of batted balls hit here turning into home runs. So that's it, the new Yankee Stadium is the easiest place to hit it out. Coors Field, as I guessed, was not really an easy place to hit home home runs. Unfortunately it's not that simple. These results may have more to do with each team's ability to hit home runs, and of their pitching staff's inability to keep the ball in the yard. So a team with lot of power and poor pitching is likely to score high on this list.
So in order to adjust for a team's ability, a new value must be found. The first step that I took was to recalculate the above table for each team while on the road. The following table shows these rates:
| Club | Team | Opponents | Total |
| PHI | 5.10% | 4.09% | 4.61% |
| CLE | 4.27% | 4.89% | 4.58% |
| TAM | 4.45% | 4.62% | 4.54% |
| BOS | 4.25% | 4.40% | 4.32% |
| NYY | 4.57% | 3.86% | 4.23% |
| TOR | 4.30% | 4.13% | 4.22% |
| MIL | 3.71% | 4.69% | 4.21% |
| DET | 4.02% | 4.27% | 4.14% |
| TEX | 4.70% | 3.58% | 4.14% |
| KAN | 3.63% | 4.65% | 4.13% |
| SDG | 3.56% | 4.55% | 4.05% |
| SEA | 3.69% | 4.23% | 3.95% |
| COL | 4.63% | 3.24% | 3.92% |
| ARI | 4.04% | 3.76% | 3.89% |
| WAS | 3.71% | 3.90% | 3.80% |
| BAL | 2.79% | 4.79% | 3.78% |
| MLB Average | 3.63% | 3.83% | 3.73% |
| MIN | 3.28% | 4.17% | 3.72% |
| STL | 4.15% | 3.18% | 3.67% |
| CHA | 3.55% | 3.66% | 3.60% |
| CIN | 2.88% | 4.27% | 3.57% |
| FLA | 3.33% | 3.72% | 3.52% |
| LAA | 3.57% | 3.45% | 3.51% |
| HOU | 2.83% | 4.21% | 3.50% |
| CHN | 3.62% | 4.01% | 3.39% |
| LAD | 3.23% | 3.45% | 3.33% |
| OAK | 2.72% | 3.90% | 3.29% |
| ATL | 3.47% | 3.02% | 3.25% |
| PIT | 2.42% | 3.89% | 3.17% |
| SFG | 2.54% | 3.83% | 3.14% |
| NYM | 1.98% | 3.47% | 2.71% |
In this table it can be seen that the Phillies had the highest rate of batted balls becoming home runs. This was largely due to their ability to hit home runs at a high rate. While on the road, 5.1% of batted balls by the Phillies became home runs. While at home, only 5.02% of their batted balls were home runs. Their opponenets did benefit by playing in Philly, with 4.42% of batted balls at the Bank becoming home runs and only 4.09% becoming home runs in Phillies' away games.
The next step is to divide the data in the two tables to determine the increase (or decrease) in rate of home runs to batted balls when a team is in it's home park. If there is an increase in thee ratios when playing at home, then playing in that stadium is beneficial to hitting home runs. The following table shows the ratios:
| Club | Stadium | Team | Opponents | Total |
| NYY | Yankee Stadium III | 1.3056 | 1.1962 | 1.2519 |
| CHA | Comiskey Park II | 1.3416 | 1.1034 | 1.2201 |
| LAA | Angel Stadium of Anaheim | 1.1240 | 1.3148 | 1.2180 |
| CIN | Great American Ballpark | 1.5495 | 0.9856 | 1.2118 |
| TEX | Rangers Ballpark in Arlington | 1.2330 | 1.1252 | 1.1769 |
| BAL | Oriole Park at Camden Yards | 1.4903 | 0.9230 | 1.1341 |
| CHN | Wrigley Field | 1.0678 | 0.9334 | 1.1240 |
| MIL | Miller Park | 1.3014 | 0.9704 | 1.1140 |
| FLA | Dolphin Stadium | 1.2000 | 1.0060 | 1.0988 |
| MIN | Hubert H. Humphrey Metrodome | 1.2859 | 0.9264 | 1.0865 |
| NYM | Citi Field | 1.1203 | 1.0393 | 1.0776 |
| HOU | Minute Maid Park | 1.2611 | 0.9129 | 1.0592 |
| TOR | SkyDome | 1.0866 | 0.9850 | 1.0360 |
| PHI | Citizens Bank Park | 0.9838 | 1.0789 | 1.0229 |
| MLB Average | 1.1026 | 0.9469 | 1.0220 | |
| ARI | Chase Field | 1.0083 | 1.0166 | 1.0115 |
| COL | Coors Field | 0.9919 | 1.0183 | 1.0022 |
| PIT | PNC Park | 1.4016 | 0.7524 | 0.9945 |
| BOS | Fenway Park | 1.2665 | 0.7404 | 0.9943 |
| DET | Comerica Park | 1.0596 | 0.9325 | 0.9942 |
| SFG | AT&T Park | 1.2255 | 0.8025 | 0.9834 |
| OAK | Network Associates Coliseum | 1.1973 | 0.7875 | 0.9600 |
| TAM | Tropicana Field | 1.1169 | 0.8009 | 0.9511 |
| WAS | Nationals Park | 0.9643 | 0.9162 | 0.9393 |
| SEA | Safeco Field | 0.9481 | 0.8310 | 0.8870 |
| LAD | Dodger Stadium | 0.9851 | 0.7783 | 0.8815 |
| ATL | Turner Field | 0.9157 | 0.8462 | 0.8812 |
| SDG | PetCo Park | 0.8576 | 0.6942 | 0.7679 |
| STL | Busch Stadium II | 0.7373 | 0.7589 | 0.7429 |
| KAN | Kauffman Stadium | 0.7897 | 0.6460 | 0.7110 |
| CLE | Jacobs Field | 0.7257 | 0.6239 | 0.6706 |
As it turns out, new Yankee Stadium is the easiest stadium in the Major Leagues to hit a home run, with 25.19% more batted balls landing in the seats than in Yankee away games. Although Yankee Stadium provided the biggest increase in home run rate, the Yankees didn't benefit as much as some other teams. The rate of home runs was 55% higher at home for the Cincinnatti Reds than when they were on the road. Their opponents actually hit homeruns at a slightly lesser rate, when coming into Great American Ballpark. As it turns out, the Rockies had a tougher time in 2009 hitting home runs while on the road, than while at Coors. Their opponents did benefit slightly, but overall the rate was nearly the same as in away games.
This analysis provides a new look on whether or not a stadium really is a good home run park or not. Unlike park factor, which only considers the amount of homeruns per game, this method looks deeper and find the number of homeruns per batted ball. This is important since other factors may lead to increased number of plate appearances per game, in certain stadiums. The additional plate appearances add to the number of homeruns, thus slightly inflating the home run park factor. Like park factor, there is still a flaw which I will discuss further in a future post. Until then, hopefully I have shed some light on which ballparks really are home run friendly and which are not.
