Hard hit rate and xFIP
If you’ve been reading the Daily Fantasy Rundown, you know that we often refer to a pitcher’s xFIP. What is xFIP? Simply put it’s an ERA estimator. It tells you what a pitcher’s ERA should be based on their K, BB and GB rates. In order to do that, they assume league averages for what we often call the three primary “luck” stats: BABIP, HR/FB rate and LOB%. We often use the gaps between a pitcher’s ERA and their xFIP to help determine if their ERA will rise or fall moving forward, assuming the same skills.
Unfamiliar with some of these terms? Check out our glossary page.
Research has shown that a pitcher controls his K, BB and GB rates but his BABIP, HR/FB rate and LOB% are mostly outside of a pitcher’s control and will regress towards league averages over time. That’s the reasoning behind xFIP. It’s based on isolating what a pitcher controls and normalizing what a pitcher doesn’t control.
However, as we get better and more sophisticated data that is readily available, it makes sense to move away from the hard line stance that a pitcher doesn’t have any control over balls in play or percentage of fly balls that go for home runs. I don’t think anyone ever fully believed this to be true. It was just that for the most part it was true and it was better to accept some errors by assuming this for everyone, rather than arbitrarily picking and choosing who we felt xFIP applied to and who it didn’t. Now it’s easy for us to whip up FanGraphs.com and look at things such as velocity, LD rate and IFFB rate, which all have a correlation to a pitcher’s BABIP and HR/FB rates.
Today, I want to take a look at one of their newest additions: soft hit and hard hit rate. The goal will be to:
1) See if there is a correlation between that data and pitchers that are either outperforming or underperforming their xFIP
2) More confidently spot pitchers we expect to improve or decline moving forward on the basis of luck