Understanding Analytics: Basic Stats
K%, BB%, K/9, BB/9, HR/9, PA/HR
As a guy who spends quite a bit of time writing about baseball analytics, I find myself constantly throwing out different metrics in posts. My boy D-Smitty let me know that it would be a good idea to have some kind of hub to link to with a repository of explanations for what I’m talking about.
In a few different posts, I’ll go through various metrics and give the long and short of it. Let’s start with some basics.
Strikeout Rate (K%)
What is it: A measure of how often a hitter strikes out
Formula: SO/PA
2021 League Average: 23%
Breakdown for hitters:
Elite: < 15%
Good: 15%-21%
Average: 21%-25%
Bad: 25%-30%
Awful: > 30%
Breakdown for pitchers:
Elite: > 30%
Good: 25%-30%
Average: 21%-25%
Bad: 15%-21%
Awful: < 15%
Walk Rate (BB%)
What is it: A measure of how often a hitter walks
Formula: BB/PA
2021 League Average: 8.5%
Breakdown for hitters:
Elite: > 12%
Good: 10%-12%
Average: 7%-10%
Bad: 5%-7%
Awful: < 5%
Breakdown for pitchers:
Elite: < 5%
Good: 5%-7%
Average: 7%-10%
Bad: 10%-12%
Awful: > 12%
Lots of times, for pitchers, you’ll see these metrics represented by strikeouts per nine (K/9) or walks per nine (BB/9).
The difference is that those metrics only look at outs the pitcher gets. The denominator is innings pitched (which means outs recorded times three).
Example: A pitcher inning goes like this: 2B, K, HR, 2B, 2B, K, HR, Flyout
Not a good inning, but he got two strikeouts - giving a K/9 of 18 (2 strikeouts times 9, divided by 1 inning). That’s a great K/9. The K% on the other hand would be 2 divided by 8 batters faced, 25% - a much more average number.
For this reason, K% and BB% are superior at telling you what happened on the field - so it’s best to default to those two.
Home Runs Per 9 (HR/9)
What is it: A measure of how often a pitcher allows a home run
Formula: (HR/IP) * 9
2021 League Average: 1.23
Breakdown:
Elite: < 0.75
Good: .75 - 1.1
Average: 1.1 - 1.3
Bad: 1.3-1.75
Awful: > 1.75
Plate Appearances Per Home Run (PA/HR)
This is one that not many people use, I have actually only ever seen myself referencing it, but I think it’s good.
What is it: A [better] measure of how often a pitcher allows a home run
Formula: Plate Appearances/Homers Allowed
Plate Appearances for pitchers will often be called “Total Batters Faced” (TBF) or “Batters Faced” (BF)
2021 League Average: 30.7
Breakdown for Pitchers:
Elite: > 40
Good: 36 - 40
Average: 24 - 36
Bad: 20-24
Awful: < 20
Breakdown for Hitters:
Elite: < 20
Good:20-24
Average: 24 - 36
Bad: 36 - 40
Awful: > 40
Tweet @JonPGH to request more stats to be written up.