xFIP
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Stat of the Week
by Peter Liubicich
xFIP
This post was written by Peter Liubicich on September 10, 2012
Posted Under: Stat of the Week

As we enter the final three weeks of the season, the expansion of the wild card is continuing to look like a wise decision by Bud Selig to expand the interest of different baseball markets in the MLB season through the end of September.  15 teams (8 in the American League and 7 in the National League) have the opportunity to be playing after the 162nd game in the season, with all of them within at least 2.5 games of the division lead or the final wild card spot.  Also as a side note, don’t look now but the Phillies are only 6.5 games out and don’t be surprised if they make a final push to make the postseason thanks to the expanded playoffs.

The approved way of evaluating pitchers is through Defensive Independent Pitching Statistics (DIPS) to see the true effectiveness of a pitcher on the aspects of the game they can control and take out the variables in the game of baseball that are not in their hands (i.e. defensive ability behind them, luck, umpires, etc.)  The first defensively independent pitching statistic we looked at was Fielding Independent Pitching (FIP) which it evaluates a pitcher on the statistics only they can control, home runs, walks, Hit by Pitch, intentional walks, strikeouts and innings pitched.  This week we will look at a variation of FIP, called Expected Fielding Independent Pitching (xFIP) which was created by Dave Studeman of The Hardball Times.

xFIP is defined by The Hardball Times as “an experimental stat that adjusts FIP and “normalizes” the home run component. Research has shown that home runs allowed are pretty much a function of flyballs allowed and home park, so xFIP is based on the average number of home runs allowed per outfield fly. Theoretically, this should be a better predictor of a pitcher’s future ERA.”

The formula for xFIP courtesy of FanGraphs:

xFIP = ((13*(FB% * League-average HR/FB rate))+(3*(BB+HBP))-(2*K))/IP + constant

Instead of using a pitcher’s actual home run total in a season, xFIP instead replaces it with their Fly ball Percentage times the League average HR/FB rate.  What this does is estimating what a pitcher’s home run total will be next year based on their historical fly ball percentage.  This allows teams to evaluate pitchers they might want to sign or trade for in the offseason and give them a better idea of how well they will perform in the future.  While xFIP certainly isn’t a perfect crystal ball it is one of the best pitching metrics to predict a pitcher’s future performance and is only outmatched by SIERA, which we will cover in the future.  Check back on Thursday where we will evaluate xFIP and it’s ability to predict different pitcher’s FIP and ERA this season.

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  1. SIERA  on October 22nd, 2012 @ 3:32 pm

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