A statistic in baseball that measures the number of home runs given up per nine innings and is the average quantity of home runs that a pitcher gives up for every nine innings pitched. The number is figured by multiplying how many home runs he gave up by nine, then dividing that figure by the quantity of innings he pitched.
As far as baseball statistics go, this is one of the easier ones to figure out. For instance, if a pitched has pitched three innings and allowed two home runs, then take the two home runs and multiply it by nine (18), then take that figure (18) and divide that by the three innings he pitched to get your result, which would be a HR/9 of 6 (which BTW would be very bad!). Obviously, the lower the percentage, the better job the pitcher does of keeping the ball in play, and the higher his ground ball percentage probably is. A ball can't leave the park if it doesn't get off the ground. Tops all time is Jim Devlin, whose HR/9 ended at .0448. Interesting, one of the greatest hitters of all time, Babe Ruth, is 13th in career HR/9 as a pitcher, with a figure of .0737.