Walks and hits per inning pitched

In baseball statistics, walks plus hits per inning pitched (WHIP) is a sabermetric measurement of the number of baserunners a pitcher has allowed per inning pitched. WHIP reflects a pitcher's propensity for allowing batters to reach base, therefore a lower WHIP indicates better performance. WHIP is calculated by adding the number of walks and hits allowed and dividing this sum by the number of innings pitched.

The stat was invented in 1979 by writer Daniel Okrent, who called the metric "innings pitched ratio" at the time. Okrent excluded hit batsmen from the numerator of baserunners allowed since Sunday newspapers did not include hit batsmen in their statistical updates. WHIP near 1.00 or lower over the course of a season will often rank among the league leaders in Major League Baseball (MLB).

While earned run average (ERA) measures the runs a pitcher gives up, WHIP more directly measures a pitcher's effectiveness against batters. WHIP accounts for pitcher performance regardless of errors and unearned runs.

WHIP is one of the few sabermetric statistics to enter mainstream baseball usage.On-base plus slugging, or OPS, a comparable measurement of the ability of a hitter, is another example of comparison. In addition to its use in live games, the WHIP is one of the most commonly used statistics in fantasy baseball and is standard in fantasy leagues that employ 4×4, 5×5, and 6×6 formats.

...
Wikipedia