H/9 represents the average number of hits a pitcher allows per nine innings pitched. It is determined by dividing a pitcher's hits allowed by his innings pitched and multiplying that by nine. It's a very useful tool for evaluating pitchers, whose goal is to prevent runs, which are usually scored by hits.
Though it's closely correlated with opponents' batting average, hits per nine is based solely on the number of outs a pitcher records, rather than the number of at-bats by his opponents. This is important because H/9 takes into account the second out on double plays, sacrifices and other outs that occur without an official at-bat being recorded -- such as outfield assists. Walks, hit by pitches and other means of reaching base do not play a factor in H/9.
In A Call
"hits per nine"