Defense independent pitching statistics
In baseball, defense-independent pitching statistics (DIPS) measure a pitcher's effectiveness based only on statistics that do not involve fielders (except the catcher). These include home runs allowed, strikeouts, hit batters, walks, and, more recently, fly ball percentage, ground ball percentage, and (to much a lesser extent) line drive percentage. By focusing on these statistics, which the pitcher has almost total control over, and ignoring what happens once a ball is put in play, which the pitcher has little control over, DIPS can offer a clearer picture of the pitcher's true ability.
Originally, the most controversial part of DIPS was the idea that pitchers have little influence over what happens to balls that are put into play. But this has since been well established (see below), primarily by showing the large variability of most pitchers' BABIP from year to year. In fact, the outcome of balls in play is dictated largely by the quality and/or arrangement of the defense behind the pitcher, and by a good deal of luck. For example, an outfielder may make an exceptionally strong diving catch to prevent a hit, or a base runner may beat a play to a base on a ball thrown from a fielder with sub-par arm strength.
Origin of DIPS 
In 1999, Voros McCracken became the first to detail and publicize these effects to the baseball research community when he wrote on rec.sport.baseball, "I've been working on a pitching evaluation tool and thought I'd post it here to get some feedback. I call it 'Defensive Independent Pitching' and what it does is evaluate a pitcher base[d] strictly on the statistics his defense has no ability to affect. . ." . Until the publication of a more widely read article in 2001, however, on Baseball Prospectus, most of the baseball research community believed that individual pitchers had an inherent ability to prevent hits on balls in play. McCracken reasoned that if this ability existed, it would be noticeable in a pitcher's 'Batting Average on Balls In Play' (BABIP). His research found the opposite to be true: that while a pitcher's ability to cause strikeouts or allow home runs remained somewhat constant from season to season, his ability to prevent hits of balls in play did not.
To better evaluate pitchers in light of his theory, McCracken developed "Defense-Independent ERA" (dERA), the most well-known defense-independent pitching statistic. McCracken's formula for dERA is very complicated, with a number of steps. DIPS ERA is not as useful for knuckleballers and other "trick" pitchers, a factor that McCracken mentioned a few days after his original announcement of his research findings in 1999, in a posting on the rec.sport.baseball.analysis Usenet site on November 23, 1999, when he wrote: "Also to [note] is that, anecdotally, I believe pitchers with trick deliveries (e.g. Knuckleballers) might post consistently lower $H numbers than other pitchers. I looked at Tim Wakefield's career and that seems to bear out slightly".
In later postings on the rec.sport.baseball site during 1999 and 2000 (prior to the publication of his widely-read article on BaseballProspectus.com in 2001), McCracken also discussed other pitcher characteristics that might influence BABIP. In 2002 McCracken created and published version 2.0 of dERA, which incorporates the ability of knuckleballers and other types of pitchers to affect the number of hits allowed on balls hit in the field of play (BHFP).
Controversy and acceptance 
Controversy over DIPS was heightened when Tom Tippett at Diamond Mind published his own findings in 2003. Tippett concluded that the differences between pitchers in preventing hits on balls in play were at least partially the result of the pitcher's skill. Tippett analyzed certain groups of pitchers that appear to be able to reduce the number of hits allowed on balls hit into the field of play (BHFP). Like McCracken, Tippett found that pitchers' BABIP was more volatile on an annual basis than the rates at which they gave up home runs or walks. It was this greater volatility that had led McCracken to conclude pitchers had "little or no control" over hits on balls in play. But Tippett also found large and significant differences between pitchers' career BABIP. In many cases, it was these differences that accounted for the pitchers' relative success.
However, improvements to DIPS that look at more nuanced defense-independent stats than strikeouts, home runs, and walks (such as groundball rate), have been able to account for many of the BABIP differences that Tippet identified without reintroducing the noise from defense variability.
Despite other criticisms, the work by McCracken on DIPS is regarded by many in the sabermetric community as the most important piece of baseball research in many years. As Jonah Keri wrote in 2012, "When Voros McCracken wrote his seminal piece on pitching and defense 11 years ago, he helped change the way people — fans, writers, even general managers — think about run prevention in baseball. Where once we used to throw most of the blame for a hit on the pitcher who gave it up, McCracken helped us realize that a slew of other factors go into whether a ball hit into play falls for a hit. For many people in the game and others who simply watch it, our ability to recognize the influence of defense, park effects, and dumb luck can be traced back to that one little article".
DIPS ERA was added to ESPN.com's Sortable Stats in 2004.
Alternate formulae 
Each of the following formulas uses innings pitched (IP), a measure of the number of outs a team made while a pitcher was in the game. Since most outs rely on fielding, the results from calculations using innings pitched are not truly independent of team defense. While the creators of DICE, FIP and similar statistics all suggest they are "defense independent", others have pointed out that their formulas involve innings pitched (IP). Innings pitched is a statistical measure of how many outs were made while a pitcher was pitching. This includes those made by fielders who are typically involved in more than two thirds of the outs. These critics claim this makes pitchers' DICE or FIP highly dependent on the defensive play of their fielders.
In that equation, "HR" is home runs, "BB" is walks, "HBP" is hit batters, "K" is strikeouts, and "IP" is innings pitched. That equation gives a number that is better at predicting a pitcher's ERA in the following year than the pitcher's actual ERA in the current year.
In that equation, "HR" is home runs, "BB" is walks, "K" is strikeouts, and "IP" is innings pitched. That equation usually gives you a number that is nothing close to a normal ERA, so the equation used is more often (but not always) this one:
That equation gives a number that is much closer to a pitcher's potential ERA.
The Hardball Times, a popular baseball statistics website, uses a slightly different FIP equation, instead using 3*(BB+HBP-IBB) rather than simply 3*(BB) where "HBP" stands for batters hit by pitch and "IBB" stands for intentional base on balls.
Dave Studeman of The Hardball Times derived Expected Fielding Independent Pitching (xFIP), a regressed version of FIP. Calculated like FIP, it replaces a pitcher's actual homerun total with an expected homerun total (xHR), where xHR is calculated using the league average of 10.6% HR/FB (home runs per fly ball). xFIP has the highest correlation with future ERA of all the pitching metrics
See also 
- Baseball statistics
- Defense-Independent ERA
- Defense-Independent Component ERA
- Voros McCracken
- Voros McCracken, "Pitching and Defense: How Much Control Do Hurlers Have?," BaseballProspectus.com, January 23, 2001.
- Defense Independent Pitching Stats Part II
- http://www.baseballthinkfactory.org/files/newsstand/discussion/vorosmccracken_me_being_arrogant_again/P100/ in item 188
- BBTF's Primate Studies Discussion :: DIPS Version 2.0
- Defense Independent Pitching Stats, Version 2.0 Formula
- Diamond Mind Baseball
- Jonah Keri, "Fantasy Fiesta: Pitching Stock Tips," Grantland, June 7, 2012.
- ESPN Sortable Stats
- For an extended overview of the development of DIPS and alternative formulas, see Dan Basco and Michael Davies, "The Many Flavors of DIPS: A History and an Overview," Society for American Baseball Research, Baseball Research Journal, Fall 2010, Vol. 32, Issue 2. [retrieved 2-26-2013]
- Sports Mogul | Official Site for Baseball Mogul and Football Mogul | Online Multi-Player Games for Fantasy, Rotisserie and Computer Sports Fans
- FIP — Hardball Times Glossary.
- xFIP — FanGraphs Sabermetrics Library.