Wednesday, May 7, 2014

Did the cold springs in Milwaukee cost Hank Aaron a lot of home runs?

Here is something Bill Deane asked on the SABR list:

"Hank Aaron was heard saying that the cold springs in Milwaukee cost him a lot of home runs, as it was hard to hit the ball out of County Stadium in the first couple of months of the season. Any numbers on Aaron's HR frequency in his home park, 1954-65, by month?"

Here are his HR percentages, home and away, for each month over this time period:

April: 4.76%, 7.44%
May: 4.60%, 5.96%
June:  5.97%, 5.91%
July: 6.61%, 6.80%
Aug: 4.41%, 5.29%
Sep: 6.07%, 3.70%

So it sure looks like "County Stadium in the first couple of months of the season" cost him some HRs.

Using the Baseball Reference Play Index and game logs, I looked at HR percentages in April and non-April for 1954-65 for the Braves, home and away. The percentages below include both what the Braves hitters did and what their pitchers allowed

April home: 2.62%
April road: 3.35%

Non-April Home: 2.64%
Non-April Road: 3.08%

So it looks like HR% was lower at County stadium than elsewhere during those years. The gap was slightly larger in April. Haven't had a chance to look at May by itself. Probably won't be much different from April or non-April.

In April and May during those years, Aaron had 252 ABs at home in April and  ABs 607 in May. How many HRs would he have hit if he had the same % as on the road?

April: 252*.0268 = 6.75
May: 607*.0146 =  8.86

That totals up to about 15. But the road % in April of 7.44% is a bit fluky. And maybe I should be using the % differentials for all players. Maybe it should be less than 15.


Bill Deane said...

Thanks for checking, Cyril. Here's another way to look at it: during his years with Milwaukee's County Stadium as his home park (1954-65, 1975-76), from June 1 to the end of each season, Aaron hit 157 homers at home, 149 on the road, or 5.4% more at home. But in April-May, he had 38 homers at home, 76 on the road. If he had maintained his 1.054 home-road ratio for those months, he would have had 80 home HRs. So, he conceivably lost about 42 HR due to the cold Milwaukee springs.

Cyril Morong said...

From 1954-65, Aaron had 859 ABs in home games during April/May and 1034 in road games. So he had only 45.4% of his ABs at home.

In the rest of the months, he had 2656 away and 2531 home. So then he had 48.8% of his ABs at home.

So his home ABs were almost even after May 31. That should reduce the estimate since Aaron would not be quite getting as many home ABs in April/May as we would think

And if, during 1954-65, we add 38 HRs to his home total, then he has 78 HRs in 859 ABs. That would be a HR% of 9.08%. That seems pretty high.

I got him with 40 HRs at home in Aril/May from Baseball Reference's Play Index