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 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.[1] It is a measure of the bases on balls ability of a pitcher.