It requires but a single digit to understand how good Wade Davis has been over the last couple years. Scan the ERA column for this year or last, and the first thing with which you’re greeted is the number zero. You can stop right there. After the zero, the other digits don’t matter. For all intents and purposes, an ERA of 0.34 is the same thing as an ERA of 0.76 is the same thing as an ERA of 0.93. Whatever the number, as long as it starts with a zero, it signifies that the pitcher in question is allowing fewer than one run per nine innings, and it doesn’t get any better than that.

Sometimes, with metrics like Fielding Independent Pitching, it doesn’t even take a digit. It just takes a symbol, and you can stop reading. Like with Hector Rondon, all you have to see is the minus sign. Hector Rondon’s FIP this season is -0.15. That’s negative zero point one five. Rondon has broken the run estimator that is Fielding Independent Pitching.

Of course, even though it feels like we’ve been saying it for a while, it’s still early. And not only is it early, but Rondon is a reliever, and so the sample is even smaller. He’s thrown 13 innings. This means very little! But it is fun! And if the Chicago Cubs had one area that might’ve been viewed as a potential future weakness before the season began, it might’ve been the back end of the bullpen. Rondon, Pedro Strop and Justin Grimm have been great in recent years, but they didn’t have a Kenley Jansen or Craig Kimbrel-type name back there.

Well, nobody’s matched what Rondon’s done thus far. He’s faced 43 batters, struck out 21, walked none, and allowed zero home runs. Only four batters have reached against Rondon — all singles.

The disclaimers: he’s not throwing any harder, he hasn’t added any new pitches, he hasn’t generated any soft contact, and his BABIP is .182. Of course there’s some fluky stuff going on; he’s thrown 13 innings and we’re talking about a guy with a negative FIP.

What we’re seeing here is perhaps some improved command, working more on the edges than around the middle, and perhaps some deception — batters are swinging less than ever, even though he’s throwing more strikes than ever, and he’s currently got baseball’s second-highest called strike rate.

Going to a bigger sample, we can point out that, over the last calendar year, Rondon’s 1.17 ERA is second among all relievers, as is his FIP-based WAR, so it’s not like this is coming out of nowhere. Rondon has truly been one of baseball’s elite relievers as of late, and he probably doesn’t get enough credit for how good he’s been. For now, everything is still too muddy to tell whether Rondon’s made any significant changes since the end of last season, but it’s always fun to point out when a number that’s supposed to be positive is prefaced by a minus sign. So, congrats, Hector Rondon. You’ve broken FIP for the first month of baseball.