K/9 rate measures how many strikeouts a pitcher averages for every nine innings pitched. It is determined by dividing his strikeout total by his innings pitched total and multiplying the result by nine.
Because a strikeout is so straightforward -- with no chance of error or bad luck, like on a ball in play -- a pitcher's K/9 rate reveals a lot about his success. However, there are many successful pitchers who get by with lower K/9 rates by inducing a high rate of ground balls and/or soft contact.
K/9 rate tells us a lot, but it's important to note the difference between starters and relievers within the statistic. Because relievers generally pitch for such a short period of time and aren't as concerned about conserving pitches, they can throw with higher intensity for each batter. As a result, relief-pitcher K/9 numbers are generally higher than those of starting pitchers.
In A Call
"K's per nine," "K-rate per nine," "strikeout rate per nine"