A pitching statistic in baseball applied for pitcher that measures the number of batters they walk, which occurs when a pitcher puts a batter on first base by throwing four balls, per nine innings of play. This number includes total walks including intentional walks. BB/9 is derived by multiplying the pitcher's walks by nine and dividing by the total number of innings the pitcher has thrown.
Also referred to as "Walk Rate."
BB/9 is used to evaluate a pitcher's ability at preventing batters from getting on base where this statistic considers that a pitcher who gives up fewer walks will give up fewer runs. One consideration with this stat is that it fails to account for intentional walks but on average, starting pitchers throw less than 10 intentional passes each season. While perhaps, not viewed, with the same importance as other pitching statistics (Walks/Hits per Innings Pitched, or ERA), BB/9 is a vital statistic in evaluating a pitcher.