Calculating Baseball Stats - Pitcher's Strikeout Per Nine Innings (K/9)

Strikeouts per Nine Innings, or (K/9) is a very simple statistic to calculate, but don't let it's simplicity fool you - it can say a lot about a pitcher's effectiveness. As the name suggests, K/9 is simply a ratio of the number strikeouts a pitcher has per nine innings (a complete regulation length baseball game).

To calculate Strikeout per Nine Innings, use the following formula:

Strikeouts per Nine Innings = (number of strikeouts) / (Innings Pitched) X 9

K/BB is denoted as a number followed by a decimal point with two numbers after the decimal. For example, a pitcher who strikes out 150 in a season in 175 innings would have a K/9 rating of 7.71 (150/175 x 9).

In 2005, Mark Prior of the Chicago Cubs led the National League (and the majors) in Strikeouts per Nine Innings, with a 10.15 rate. He struck out 188 hitters in 166.6 innings pitched. In the American League, Johan Santana of the Minnesota Twins led the league with a K/9 rate of 9.25. He struck out 238 hitters in 231.6 innings pitched. It was Santana's second straight season leading the league in K/9.

Many baseball experts claim that strikeout rate is not that important. They argue that a strikeout is just another out, and no different than a groundout or fly out. Noted baseball analyst Bill James has found much evidence that strikeout rate is important, however. The ability to "trick" or overpower hitters make up a good part of a pitcher's ability to be successful over a long period of time. James has noted that a pitcher with a K/9 rating of below 4.50 is very unlikely to have a long, successful career. He notes that several pitchers have had success slightly above this mark (such as Tom Glavine, Tommy John, and Jimmy Key), but that below that threshold, it is very rare. A high strikeout rate often translates into success, as it did with Santana (16-7, 2.87 ERA) and Prior (11-7, 3.67 ERA in an injury shortened season). Such star pitchers as Randy Johnson, Pedro Martinez, and Roger Clemens have been perennially among the league leaders in K/9.

Johnson, a five time Cy Young award winner and a future Hall of Famer, dominates the list of top K/9 seasons of all time, holding seven of the top 10 seasons all time, including the #1 spot with a 13.41 rate. Pedro Martinez appears twice on the list at number two (3.20) and number nine (11.78). Kerry Wood, who shares the major league record with 20 strikeouts in a single nine-inning game, has the third highest single season total at 12.58.

Johnson, Martinez, and Wood also hold the top spots on the career K/9 rankings for pitchers with over 1,000 innings pitched. Johnson holds the top spot at 10.95, followed by Wood at 10.44, and Martinez at 10.25.

As you can see, Strikeouts per Nine Innings are an easy statistic to calculate, but it is very valuable when estimating the value and future success of pitchers.