Teams win 54% of their home games. High? Low? Why? Wednesday, February 3, 2016
FIP blah, blah, blah. Thursday, February 4, 2016
For about 15 years conventional wisdom among the smart guys has been that Strike Outs, Walks, Home Runs are controlled by the pitchers and are not random as are balls put in play for the fielders. This despite two obvious things:
- balls and strikes are decided, not by the pitchers, but by the plate umpires
- home run distances differ not just from park to park but also within each park.
Strike Outs, Walks, Home Runs are random.
See the two posts shown above for more on that.
I thought it might be helpful to examine the National League for the years that Mike Schmidt played since the parks were at least symmetrical and that might shed light on the issues of randomness and the home team winning 54% of its game. The parks had very similar but not necessarily identical distances and wall heights.
These things jump out in the very first year, 1972:
- home winning percentage: 49.4%
- plate umpire SO/W: Art Williams was 25% higher than Shag Crawford and Bruce Froemming.
- plate umpire SO9: Art Williams was 20% higher than Andy Olsen and 12% higher than the closest ump, Tom Gorman
- home/road ERA are really close: 3.36 and 3.56
- higher HR rate on the road for pitchers, which means higher at home for batters.
Click this link to view underlying data drawn from baseball-reference.com
For SO/W and SO9 the percent difference between the high (hi) and low (lo) umpires uses the lo as base.
For ERA and HR/AB the percent difference between home and road uses home as base.
| Ump%dif | Ump%dif | % dif | % dif | |
| Year | SO/W | SO9 | ERA | HR/AB |
| min | 25.00% | 18.00% | -18.24% | -15.60% |
| max | 87.68% | 47.50% | -2.81% | 4.76% |
| ave | 67.70% | 30.91% | -10.66% | -4.03% |
| StDev | 15.88% | 7.04% | 3.63% | 5.39% |
SO and W should have little to do with symmetrical parks but the variation for plate umpires is shocking. For ERA and HR rate the differences seem to favor home cooking. Pitchers ERA average 10.66% better at home and batter HR rate averages 4.03% better at home.
The Home Run Rate is difficult to explain. Mike's Schmidt HR/AB: home 6.6%, road 6.5%. Almost dead even.
But those seasons were five years before the start of so called inter-league play in 1994. There were separate groups of umpires for each of the two leagues, American and National.
Now with visual estimating of balls and strikes and plate umpires being graded on that their calls must be better, right? Here is the NL data for 2015:
| Ump%dif | Ump%dif | % dif | % dif | |
| Year | SO/W | SO9 | ERA | HR/AB |
| 2015 | 108.38% | 34.33% | -9.36% | -4.85% |
Yikes. The NL plate umpires in 2015 look worse than 1972-1989. Average percent difference between hi and lo umps:
SO/W exploded from a shocking 67.7% to a ridiculous 108.38%. That means that in 2015 National League games one umpire's SO/W was more than twice another's. Now that's random.
SO9 30.9% then, 33.33% now. Not much difference but still disturbingly inconsistent. One NL plate umpire in 2015 presided over 33% more SO per nine innings than a colleague. What the heck?
2015 plate umpire differences will be examined in a future post. The way in which baseball-reference.com displays umpire data for recent seasons is EXREMELY confusing. I've sent an inquiry to baseball-reference.com but have not received a reply yet. See the next post for more on this.
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