HR/9 measures how often a pitcher gives up the one outcome no defense can save him from. It is also the noisiest of the three FIP inputs — home run rates bounce year to year more than strikeout or walk rates do.

Park matters here more than anywhere else on a pitching line. The same fly ball is a home run in one stadium and a warning-track out in another, which is why xFIP exists: it replaces a pitcher’s actual home run total with what his fly ball rate would normally produce.

NUT uses actual home runs allowed, not an estimate — the runs really scored. When a pitcher’s NUT lags his strikeout and walk profile, HR/9 is usually the reason, and xFIP is the place to check whether it is likely to persist.

What is a good HR/9?

Home runs allowed are the heaviest negative in FIP, and therefore the fastest way to sink a pitcher’s NUT.

Related Stats