Walks plus Hits per Innings Pitched (WHIP) is essentially a measurement of how many base runners a pitcher allows per inning. Given that preventing base runners the fundamental role of pitchers, a rate statistic designed to tell you how many they allow definitely points you in the right direction.
That being said, WHIP is more of a quick reference statistic rather than something you want to use for full-fledged analysis. If you want to measure base runners allowed using a rate stat, OBP against is a better choice because batters faced is a better denominator than innings. WHIP is also lacking in that it treats all times on base equally, equating a walk with a home run. A statistic like wOBA against is more useful in that regard.
While WHIP is no longer at the forefront of stat-head analysis, it’s easy to calcuate and corelates relative well with more accurate statistics. Think of WHIP as something like OPS. It’s a little rough around the edges but it will generally provide a fine starting point.
WHIP is calculated exactly how you would expect:
WHIP = (Walks + Hits) / Innings
Pitching is about run prevention and run prevention is about base runner prevention, so it makes sense that you’d want to know how well a pitcher prevents base runners. Walks and hits are the two primary ways runners reach base, so turning those into a rate stat makes plenty of sense. WHIP answers the question “about how many base runners does this pitcher allow per inning?”
You might want to ask more precise questions, like “how many runners does he allow per batter faced?” or “how many bases does he allow per inning or batter faced?” but WHIP is a quick way to a similar answer and is the kind of thing that is very easy to calculate even with limited data sets. Once upon a time, that made it a very popular statistic in fantasy baseball leagues because it was more advanced than the raw outputs you were used to seeing, but didn’t require a lot of heavy lifting.
How To Use WHIP:
WHIP is a measure of base runner prevention, but it’s important to remember that base runner prevention is part pitching and part defense. The walks are mostly the pitcher’s fault, but hits vary dependig on the situation. Home runs are the fault of the pitcher but singles are shared between the pitcher and the defense. Like many pitching statistics, it’s a measure of what happened while the pitcher was on the mound, not a measure of the pitcher’s unique contributions.
However, WHIP is a better isolation of pitcher performance in many cases than something like ERA because it’s based on individual events rather than a sequence of events. In other words, it’s easier for one bad play on defense to tank your ERA than your WHIP.
Lower WHIP is better and you can use it as rough estimate of dominance. If you have access to OBP against or wOBA against, you should use those instead, however, as they are a bit more mathematically consistent with the concepts we want to measure — either the prevention of base runners or the prevention of bases themselves.
Please note that the following chart is meant as an estimate, and that league-average WHIP varies on a year-by-year basis. To see the league-average WHIP for every year from 1901 to the present, check the FanGraphs leaderboards.
Links for Further Reading: