For most purposes, FIP works as an ERA estimator. It tells you how many runs per nine innings a pitcher is responsible for if you ignore balls in play. An ERA can never be a negative number, because if you give up no runs, your ERA is 0.00, but there are special circumstances when a FIP can go subzero.

Mason Miller didn’t just go below 0.00 for a weird outing or two early in the year—his FIP lived in the negatives from April 4 to May 15. Through his first seven appearances, it was -1.67, which is apparently what happens when you strike out 19 of 24 batters faced with one walk and no home runs. At that point in the season, he’d only thrown 20 pitches called a ball, which was just one more than his strikeout total, and he didn’t allow his second hit until he faced his 31st batter. The man is doing impossible things.

What does a negative FIP mean? A 0.00 ERA means the pitcher has given up no runs, but the concept of negative runs doesn’t make sense. Does having a defense behind him make him a worse pitcher? There are unsubstantiated stories of Satchel Paige waving his teammates off the field, but Miller hasn’t done that in 2026. A negative FIP is one of baseball’s irrational numbers, like dividing by zero. It means he broke the statistic.