When you hear someone use "WHIP" in baseball talk, it doesn't mean what kind of a throwing arm a pitcher has. It's actually an acronym for Walks Plus Hits Per Innings Pitched. It's WHIP because WPHPIP just isn't as easily pronounced.
The statistic was created by baseball author Dan Okrent. Okrent is actually one of the fathers of fantasy baseball as we know it now, but he also came up with WHIP in 1979. It originally was known as IPRAT - Innings Pitched Ratio. Nobody knows who exactly changed it to "WHIP" or when it happened, but even Okrent has said he thinks it's better than IPRAT.
The WHIP metric is focused on evaluating how well a pitcher does at preventing batters from getting on base. The idea is that the more runners that get on base for every inning pitched (a higher WHIP) the greater chance that runs will be scored against the pitchers team.
The calculation of Walks Plus Hits Per Innings Pitched is fairly straight forward and is represented as a formula as such:
An example of a one-game WHIP: say a pitcher went seven innings and gave up six hits and walked one. So. 6 + 1 divided by 7 = 1.00. Over a greater period, say the pitcher had pitched 68.2 innings while giving up 70 hits and walking 26 would result in a WHIP of 1.41 (70 + 26 divided by 68.2).
When evaluating the WHIP number, it's important to note that the league average for pitchers is usually in the range of 1.30-1.40. League leaders will usually be right around 1.00 for the season.
The career WHIP record is held by Addie Joss, pitched from 1902-1910, who over 257 career games had a WHIP of 0.968. The best single season WHIP was produced by Boston Red Sox pitcher Pedro Martinez who had a 0.737 WHIP over the 2000 season (minimum of 1 IP per team game).
Benefit of WHIP
As mentioned previously, Walks Plus Hits Per Innings Pitched is a great tool for evaluating a pitcher and his ability to prevent batters from getting on base and potentially becoming runs. As a pitcher specific metric, meaning that it mainly focuses on the actions and outcomes of the pitcher, it gives a strong insight into the pitchers ability - unlike more team measures like runs and wins, which aren't specifically in the control of the batter.
An additional benefit of WHIP is to highlight situations in which a pitcher may be either over or underrated based on more traditional pitching metrics like Earned Run Average and wins. For example, a great pitcher could be on a team with a weak offense and have a poor win record.
By not taking into account earned runs vs. unearned runs, so it's entirely possibly a pitcher could be seemingly cruising along with a low E.R.A. and a high WHIP, which would indicate that a fall back to earth would be likely imminent, since giving up a lot of hits and walks will catch up to that hurler.
When the voting is conducted for the Cy Young Award, most people tend to look at the usual categories - win totals, E.R.A., strikeouts, or even save totals (see Dennis Eckersley in 1991), if one looks at the WHIP totals of these pitchers, they are often really low even if some of the other statistics don't quite measure up.
The best examples of that occurred with three pitchers in two seasons - Zack Greinke and Tim Lincecum in '09 and Felix Hernandez in '10. When one looks at the Cy Young award winners over the years, the winners usually have extremely gaudy totals in wins, E.R.A. etc. The shinier the better - but '09 and '10 really threw that on its ear. Greinke won a modest 16 games and Lincecum won 15 games. Even more impressive: Hernandez won in '10 while winning only 13 games, which didn't even come close to showing how dominant he was that season.
The really telling thing? Greinke, Lincecum and Hernandez all had otherworldly WHIPs in those seasons: 1.073, 1.047 and 1.057.
Another thing that makes it harder for a starter to have a WHIP below 1.00 is that starters have a lot of innings pitched, so the more innings one pitches, the more chances to give up hits and walks. Since there are fewer innings for a reliever, the really dominant ones can have some WHIPs that are truly ridiculous - Eckersley had a season where he had a .603 WHIP and he had a .913 WHIP in '92 when he won the American League Cy Young AND MVP. He didn't pitch more than 80 innings as a closer, though, while Dwight Gooden pitched 276.2 innings in '85 when he had a .965 WHIP. Yes, he won the National League Cy Young Award that year.
Its best use is during a season to see if a pitcher is likely going to pitch at his current level, if he's just pitching well and is not getting results (wins, etc.) or if he's being sneaky good and is due for a fall.
On the other hand, like any statistic, it is not infallible since there are always a host of other factors that can play a part - weather, the ballpark that he's pitching in, how he feels, the alignment of the planets, etc. Is this a pitcher who can hold teams to 10 scattered singles and 8 walks over eight innings and be the beneficiary of several timely double plays or is this one who can give up five hits, but have all of them be of the long ball variety?
Okrent created a great statistic, yes, but it is not one to just be followed blindly by itself but to used in conjuntion with other statistics to evaluate pitchers.