As we approach the last month of the 2022 baseball season, I thought it would be nice to make available a live Shiny app that allows one to predict Aaron Judge’s home run season total. I’ve described the prediction process in previous posts.
The app is currently live at
https://bayesball.shinyapps.io/HomeRunPrediction2/
The only input you need is the quartiles of your prior on Aaron’s home run probability — this reflects your beliefs at the start of the 2022 season. (I don’t believe the predictions are that sensitive to this prior since these beliefs are updated with the 2022 HR data.) Currently I have set these quartiles at 0.05 and 0.09, but you can adjust these values with the slider. Using functions from the baseballr package, I read in Aaron’s current PA and HR values and the Yankees current win and loss values which I can figure out the games remaining. Today (morning of August 25), I predict (with probability 0.917) Judge will hit between 56 and 69 home runs and the chance he will break Roger Maris’ mark is 0.57.
As constructed, this app will update the prediction each day using the current data. The interested reader might enjoy visiting this app periodically and see how the predictions change as we finish out the 2022 season.
Exploring Baseball Data with R 
Hi. I have been reading your blog and I love the way you are using MLB stats and data in so many different ways. This is so cool!! I also really like how you were able to predict Aaron Judge’s home runs. Can you please come read and follow my blog? I also write about baseball.