How do you know when a knuckleball pitcher is good? It’s not an easy question to answer. We know it’s not just a matter of having a knuckleball — there have been bad knuckleball pitchers. But the pitches themselves aren’t easy to scout, and the whole idea behind an effective knuckleball is sort of the lack of consistency. There’s not a large sample of these pitchers to examine, which further complicates things. A knuckleballer is the most unusual player type in the game, someone who can be almost impossible to trust, but someone who also throws a pitch that seems almost impossible to hit.

There’s a line somewhere. There has to be. There’s a line beyond which a knuckleball pitcher is legitimately good, and maybe that’s when he throws 60 good knuckleballs out of 100, or maybe it’s when he throws 90 good knuckleballs out of 100. We’ve seen R.A. Dickey be an ineffective knuckleballer, and we’ve seen him be an effective one. The pitch gave his career a second chance, which is one of its magical aspects. At some point, I suppose, you just have to look at the numbers. The numbers will tell you when a knuckleballer is working. I don’t know of any other approach, and what the numbers are indicating is that Steven Wright has mastered the weirdest pitch in the sport.

Wright faced the Orioles Monday, and he threw a pitch that kind of went viral. I wouldn’t say it was a particularly incredible knuckleball, but only because any good knuckleball seems insane. Watch as Chris Davis flails:

Now watch again, in super slow motion:

It’s easy to let your eyes lie to you. There are a lot of moving parts in here, and I think the inclination is to exaggerate the movement on the baseball. You think you see it darting in one direction, and then suddenly darting in the other. That’s not what really happened, but nevertheless, look at the margin by which Davis whiffed. The pitch moved enough, unpredictably. For another look, here’s Wright making a fool of Mark Trumbo, who’s spent the year making fools of his own opponents:

Same pitch, basically. Trumbo swung well over the ball. Davis swung well under the ball. That tells you the batters weren’t seeing it, and this is how a knuckleball looks amazing. At its worst, a knuckleball is indistinguishable from a deliberate lob over the plate, and that’s why these pitchers are so difficult to trust, but when someone really has a feel for it, there’s no better single weapon, and it’s no mystery why. A good knuckleball is something right out of a cartoon.

The numbers, which I mentioned — Wright this year has started 10 times for the Red Sox. He’s one of 104 qualifying starting pitchers in the league, and out of that group, Wright ranks tied for eighth in ERA-, even with Madison Bumgarner and Rich Hill. Now, that’s not a huge sample, especially when we’re dealing with earned runs. So let’s stretch back to include last season, when Wright started another nine times for the Red Sox. Since the beginning of 2015, Wright’s one of 161 starting pitchers with at least 100 innings. Out of that group, he ranks alone in eighth in ERA-, between Jose Fernandez and John Lackey. Steven Wright hasn’t allowed many runs. The formula is a strange one, but you have to like the results.

With just about any other pitcher, you focus on the peripherals. And it’s not like they don’t matter at all for Wright — like anyone, he wants to get strikeouts, and limit walks. His numbers there are fine; they’re neither exceptional nor lousy. But what Wright gets to claim as an ability is getting weak contact. We’ve seen Dickey keep his ERA below his FIP. Tim Wakefield did the same thing. Out of that group of 161, Wright’s allowed the sixth-lowest BABIP. Last season, he ranked in the 87th percentile in avoiding batted balls of at least 95 miles per hour. This season, he’s in the 98th percentile — only Kenta Maeda has been better. I know Statcast isn’t perfect, and I know a cutoff of 95 is arbitrary. But it doesn’t really matter where you look, or where you draw lines. The evidence suggests Wright is challenging to square up. We all know why that would be the case.

Batters ache for predictable movement. They all have lifetimes of tracking pitches with predictable movement, and even an especially nasty slider is predictably nasty. The pitcher knows how he wants that pitch to move, and if it’s thrown right, that’s what’ll happen. Knuckleballs don’t behave like that. Wright himself doesn’t know what the ball is going to do. A knuckleball is slow enough that hitters can mostly track it, but they dance around so much getting the barrel there isn’t easy. That can lead to softer contact. Wright’s overall contact rate allowed is good, if short of fantastic. It’s the breakdown that’s unique. That group of 161 starters since last year with 100+ innings:

Wright has allowed one of the higher rates of contact out of the zone, but he’s allowed the lowest rate of contact within the zone. He’s at 76%; Max Scherzer is in second at 79%. Wright also ranks fifth in the group in zone rate, so he fairly consistently throws strikes, and batters fairly consistently miss them. Put another way — when hitters are equipped to make good contact, they whiff more than average. When hitters are equipped to make poor contact, they hit the ball more than average. This all comes from the knuckleball’s unpredictability, and it helps Wright stay out of danger. Though he isn’t a strikeout machine, and though he does run into his walks, those baserunners are tough to drive home. Where for some pitchers that can be a fluke, with Wright it’s part of the design.

I can’t imagine he’s 2.50-ERA good. Very few starting pitchers are 2.50-ERA good, especially in the American League, especially in Boston. And I acknowledge that someone like Wright is particularly hard to evaluate. If he loses that feel, the knuckleball will be bad, and then Wright himself will be bad, and that’ll show up in the statistics. But what the statistics show right now is that Wright has the knuckleball down cold. Over a stretch of 19 big-league starts, he hasn’t allowed many runs, and that’s the entire goal. It would appear that Steven Wright has mastered baseball’s silliest pitch, and that’s a pitch that leads to some of baseball’s silliest swings.