One goal of baseball metrics is to filter out as many outside influences as possible to measure individual performance.
For pitchers, metrics look beyond ERA because team defense can drive it up or down.
FIP (fielding independent pitching) has gained wide acceptance and correlates better to future ERAs than does ERA itself. There’s another step beyond FIP: xFIP (expected fielding independent pitching).
To see how this works, let’s look at Jose Quintana, who has been the 1A to Chris Sale’s 1 in the White Sox’ rotation. By traditional measures, Quintana is 5-2 with a 1.54 ERA, which leads the Ameri-can League. (Sale is second at 1.67.)
FIP factors out everything in which defense might be a factor, focusing on home runs, walks, hit-by-pitches and strikeouts.
The basic formula is 13 x HR + 3 x (BB+HBP) – 2 x K, all divided by innings pitched. Once you have that result, the total is added to a league constant. The constant, which is around 3.10 in most years, is designed to put FIP on the same scale as ERA, so 3.00 indicates a quality pitcher.
Quintana leads AL qualifiers with a 2.16 FIP, followed by the Red Sox’ David Price (2.51), the Orioles’ Chris Tillman (2.61), the Indians’ Danny Salazar (2.82) and Sale (2.82).
Quintana’s FIP is the result of strong positives all the way around. In 52⅔ innings, he has allowed only one homer. He has struck out 47 batters, walked 11 and hasn’t hit a batter.
With xFIP, Dave Studeman of the Hardball Times sought to remove a possible chance factor. Pitchers’ home-run rates on fly balls can vary wildly from season to season. Sample sizes are small, and it’s an open question about how well they reflect pitcher performance, as opposed to wind, ballpark mix, opposition and other factors. During the course of a long career, the home-run percentage usually approaches a league average that usually is between 9 percent and 10 percent of fly balls.
Instead of homers, xFIP uses the number of homers that would be expected if an average number of fly balls left the park. The formula is 13 x (fly balls x league fly-ball percentage) + 3 x (BB+HBP) – 2 x K, all divided by innings pitched, then added to the FIP constant.
Quintana has been extraordinarily successful at keeping balls in the park. With one homer allowed on 52 flies, his homer-to-fly ball rate is 1.9 percent. Using a league average of about six homers per 52 flies leads to a higher xFIP.
That takes Quintana’s xFIP to 3.47. That’s not quite as lofty as his FIP, but it’s still 10th in the AL. Price leads at 2.67, with Sale 14th at 3.59.
Nobody allows only 1.9 percent of flies to become homers for a whole season. The Twins’ Mike Pelfrey led the AL at 7.4 percent last season. But xFIP tells us that even at a more normal homer-to-fly ball rate, Quintana has had the right stuff.
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