Baseball Glossary › Walks per Nine Innings
Walks per Nine Innings (BB/9)
Walks per nine innings (BB/9) is the average number of walks a pitcher issues for every nine innings pitched. Multiply walks by 9 and divide by innings pitched. It measures control. A walk puts a runner on base without giving the defense any chance to make a play, so a lower BB/9 is almost always better.
Formula
Worked example (illustrative numbers): a pitcher walks 50 batters in 180 innings.
BB/9 = 9 x 50 / 180 = 450 / 180 = 2.5
Convert partial innings first: 180.2 IP is 180.667 innings
Athletics example: Dennis Eckersley
Dennis Eckersley, famous for his control, walked 738 batters in 3285.2 career innings (3285.667 true innings). See the full career line on the Dennis Eckersley player page.
BB/9 = 738 x 9 / 3285.667 = 2.02
Career MLB totals from our player database (MLB Stats API).
What to Know
BB/9 vs BB%: BB/9 is per inning, while walk rate is per batter faced. As with strikeouts, the per-batter version avoids distortions from how many hitters a pitcher faces per inning.
FanGraphs' rough guide, which it labels an estimate, puts about 2.9 at average, 1.9 as great and 1.5 as excellent for BB/9. Relievers tend to walk slightly more batters than starters.
Walks feed directly into WHIP, and they are the bottom half of the strikeout-to-walk ratio, one of the most common quick checks of a pitcher's command.
Frequently Asked Questions
What does BB/9 mean in baseball?
BB/9 means walks per nine innings. BB stands for base on balls, the official name for a walk, so BB/9 is the average number of walks a pitcher allows per nine innings.
How do you calculate BB/9?
Multiply walks by 9 and divide by innings pitched. A pitcher with 50 walks in 180 innings has a BB/9 of 2.5. Convert innings such as 180.2 to 180.667 before dividing.
What is a good BB/9?
As a rough guide from FanGraphs, about 2.9 is average, 1.9 is great and 1.5 or lower is excellent. These ranges are estimates and shift with league walk rates each season.
Is a lower BB/9 better?
Yes. Fewer walks means fewer free baserunners. A pitcher with a low BB/9 forces hitters to earn their way on base, which usually helps keep runs off the board.
What is the difference between BB/9 and BB%?
BB/9 counts walks per nine innings, while BB% counts walks per batter faced. BB% is often preferred because it is not affected by how many batters a pitcher faces each inning.
Do intentional walks count in BB/9?
Standard BB/9 uses total walks, which include intentional walks. Some advanced stats, such as certain versions of FIP, remove intentional walks, so check how a site defines it.
Related Terms
Sources
- MLB.com Glossary: Walks Per Nine Innings (BB/9)
- FanGraphs Sabermetrics Library: Strikeout and Walk Rates
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