A Look at xFIP and HR/FB Rates – Identifying Undervalued Pitchers

Value is everything in any money-making endeavor. Want to trade stocks? Look for value. Want to win on Draftkings? Buy low, my friend.

This week, we have explored several of the ways I search for undervalued hitters. It’s time for the pitchers to get some love.

Like BABIP, Hard%, and ISO for hitters, pitchers possess several metrics which can tell a story beyond the classic stat line (ERA, WHIP, wins, Ks).

One of my favorite pitching metrics is xFIP. This stat is relatively new and stands for Expected Fielding Independent Pitching. It attempts to take luck out of the equation and determine what a pitcher’s ERA deserves to be given his stuff and how well he is pitching.

Where can I find xFIP? What is a good xFIP? How can I find value using xFIP?

Stick around for all these answers and more. Let’s dig in!

All Pitchers Give up Fly Balls – Some are Just Unlucky

Even the groundballiest of ground ball pitchers allow a lot of pop flies. So far this season, the Padres’ Joey Lucchesi and the A’s Frankie Montas are allowing the fewest fly balls in the majors, with FB rates of 24.0% and 24.1% respectively.

This means that at least one quarter of all batted balls are hit in the air for even the stingiest of ground ball hurlers. Fly ball pitchers tend to be closer to 50%, if not higher.

Because fly balls are so common, studying every single fly ball hit over the course of one or more seasons gives us an enormous sample size. Any data we generate from these studies is going to be fairly predictive.

What we find is that the percentage of fly balls that wind up being homers is relatively constant from year-to-year. Since 2017, the league average has bounced between 12.5-14.5%. We’ll say that 13.5% of fly balls turn into home runs in today’s MLB.

This stat does not correlate very strongly to how good a pitcher is. There are some very good pitchers who are tagged with high HR/FB rates and poor pitchers who limit the dingers very well.

A certain percentage of balls put into play against you will be fly balls and a certain percentage of those will be home runs. That’s just how it is.

When a pitcher holds a 4.5% FB/HR rate, it is not because he is fooling everyone and inducing weak contact. He is simply the beneficiary of some good ole’ fashioned favorable fortune.

Likewise, when 20% of a pitcher’s fly balls are turning into home runs, he just cannot catch a break. He is probably allowing some wall scrapers and wind-aided blasts.

This is the problem that xFIP attempts to remedy. xFIP takes fielding and home run-luck out of ERA. A pitcher’s ERA is perhaps his most defining statistic. xFIP tells us what that pitcher’s ERA would be given a league-average defense and a league-average HR/FB rate.

If a pitcher has an ERA of 5 (which is not good) he is likely going to be overlooked as an early-season bust. If his xFIP is 2.50 (very solid), we know that he is just getting unlucky and is due for a resurgence.

On the flip side, xFIP can help you if you own a pitcher who is 3-0 with a 1.50 ERA. If his xFIP says his ERA should be 4.50, this player is overvalued and you should sell high on him because his numbers will likely come crashing down to earth.

Large ERA-xFIP Discrepancies in 2019

1. Zack Greinke

 

With a career HR/FB rate of 10.3%, Greinke has always skated on the lower edge of the bell curve. Through 6 starts in 2019, the 35-year-old has suffered through 24.2% of his fly balls turning into roundtrippers.

Greinke’s ERA is elevated because of this – up to 3.72 – but xFIP says it should be half a run lower – at 3.25.

2. Max Scherzer

The former Cy Young winner is off to a rocky start in 2019. A 4.45 ERA has led to a subpar 1-3 record and you know Max is not happy about it.

One look at the numbers will tell you that Scherzer deserves to have an elite stat line but that his defense has let him down. Through his first 5 starts, the 11-year vet is posting a career-high in K/9 and his second-best BB/9 season ever.

HR/FB rate is not the culprit in Scherzer’s case, as his 11.5% rate is extremely average and sustainable. It is simply the defense.

Right now, Washington’s ranks among the league’s worst and their ace is paying the price for it. xFIP says Scherzer should own a 2.55 ERA. He will get back into the 2s before 2019 is all said ‘n done.