In baseball statistics, bases on balls per nine innings pitched (BB/9IP or BB/9) or walks per nine innings (denoted by W/9) is the average number of bases on balls, (or bases on balls, walks) given up by a pitcher per nine innings pitched. It is determined by multiplying the number of bases on balls allowed by nine, and dividing by the number of innings pitched. It is a measure of the bases on balls ability of a pitcher.

Leaders

All but one of the top 25 single-season leaders in BB/9IP through 2018 pitched in the period of 1876-84. George Zettlein was the all-time single-season leader (0.2308 in 1876), followed by Cherokee Fisher (0.2355 in 1876) and George Bradley (0.2755 in 1880).Single-Season Leaders & Records for Bases On Balls per 9 IP , Baseball-Reference.com
/ref> The highest single-season modern day baseball performance was by Carlos Silva (baseball), Carlos Silva (0.4301 in 2005). The all-time career leaders in BB/9IP through 2022 were Candy Cummings (0.4731), Tommy Bond (baseball), Tommy Bond (0.4787), and Al Spalding (0.5114), all of whom played in the 1870s and 1880s. The active career leaders in BB/9IP through 2022 were Corey Kluber (1.9683), Michael Pineda (1.9719), and Hyun Jin Ryu (1.9914).Active Leaders & Records for Bases On Balls per 9 IP , Baseball-Reference.com
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References

Pitching statistics {{Baseball-stub