Marco Estrada may not have known he was on track to set a modern Major League record when he talked to reporters last week at the All-Star Game in San Diego. (He is! More on that in a second.) And he may not know why his effective fastball behaves so differently than most others, saying, "I think it's just natural, to be honest with you; I'm not holding the ball any different, it's just a normal four-seam fastball," when asked.
But Estrada definitely knows there's something unique about that pitch, and he's on the right track when he talks about how it looks coming out of his hand:
"You know, I have noticed, there are times that I'll watch a guy throwing 93, 94, and they'll put it in slow motion, and you can see the ball kind of tumble up there," Estrada said. "And I'll look at mine, and it looks kind of like a cue ball. It's just a perfect white ball. I notice my four-seamers are straight right up and down, however you want to put it... it looks like a cue ball."
We haven't used "cue ball" to describe a four-seamer that's getting the most out of its spin, but perhaps we should. We've talked a lot about spin rate around Statcast™ HQ, and it's been very useful, teaching us that high-spin fastballs tend to correlate better with swinging strikes and popups, while low-spin heaters dive and turn into ground balls.
Regardless of the terminology, Estrada has taken pretty good spin and turned into into very good movement, and that, along with his "cue ball" comment, is a pretty good indicator that he's likely got a nearly perfect spin direction -- that is, he's getting the most of out of his spin by getting it straight up and down, wasting almost none of it with side spin. It's a difficult thing to measure, but if we accept that all spin is not created equally, then pushing all of it in the right direction is a good way to set yourself apart.

Estrada's fastball spin rate of 2,413 rpm is above average, and it ranks 11th of the 82 pitchers who have thrown at least 500 four-seamers. (Justin Verlander and Max Scherzer are essentially tied for first, at 2,555 rpm.) Of course, Estrada's average velocity of 88.9 mph is 80th of those same 82, a full 9 mph slower than Nathan Eovaldi. But Estrada is successful and Eovaldi isn't, because it's not just about speed. No one in baseball gets more positive vertical movement (which is to say, a pitch that sinks less, or defies gravity more, than expected) than Estrada:
Highest four-seam vertical movement, 2016 (minimum 500 thrown)

1. Estrada, 13.1 inches
   
2. Chris Young, 12.4 inches
   
3. Clayton Kershaw, 12.0 inches
   
4. Tommy Milone, 11.9 inches
   
5. Drew Smyly, 11.7 inches
   Perhaps unsurprisingly, no one in baseball has a higher percentage of their fly balls turning into popups than Estrada (17.6 percent, just ahead of CC Sabathia and Jered Weaver), and that's extremely good, because popups are basically strikeouts. The Majors are hitting just .022 on popups, and Estrada has not allowed a hit on 44 of them this season. While it's true he doesn't pile up the strikeouts, if you consider those popups to be the equivalent of whiffs, it would push his strikeout percentage from 24.1 percent to 34.8 percent -- or the second-highest strikeout rate in baseball behind José Fernández. Obviously, that's unfair because you'd have to give the same credit to every other pitcher, but the point is clear. Strikeouts are good, but so are popups, and Estrada gets a ton.
   Now, about that Major League record Estrada is working toward: It's true, and it's a good one.
   Let's explain. Dating back to the birth of the American League way back in 1901, there have been 8,631 individual seasons by pitchers who threw enough innings to qualify for the ERA title. That's a ton of seasons from a ton of pitchers, and it includes basically all of the elite pitchers you can name from any era. Never, across more than a century of baseball, has any starter done a better job of preventing hitters from turning contact into base hits than Estrada has done this year.

That's a big claim! Let's prove it. We're basically talking about Batting Average on Balls In Play, better known as BABIP, and it measures exactly what it claims to. Setting aside strikeouts and home runs, it simply looks at balls in the field of play and shows how often they turn into hits. Obviously, a pitcher wants that number to be as a low as possible. Let's look at the top part of that leaderboard:
Lowest BABIP, Qualified Pitchers, 1901-2016

1. Estrada, 2016 Blue Jays -- .193
   
2. Ed Reulbach, 1906 Cubs -- .196
   
3. Dave McNally, 1968 Orioles -- .201
   
4. Tommy Byrne, 1949 Yankees -- .205
   
5. Carl Lundgren, 1907 Cubs -- .207
   A quick look at the other names on that list should tell you a little bit the extremes we're talking about here. McNally's season came in the famed "Year of the Pitcher," 1968. Reulbach and Lundgren played so long ago that the sport they played was barely even baseball -- they literally pitched in front of Tinker, Evers and Chance. For more contemporary context, the next-lowest BABIP this year is .231 from Julio Teheran, a pretty large 38-point difference. The highest marks from qualified pitchers this year are Robbie Ray (.359) and Matt Harvey (.353), and it doesn't take an advanced degree to know that the more balls in play that turn into outs, the better off you are.
   Now, depending on the situation, that can show good (or bad) luck or good (or bad) defense, but in some cases, it can be a skill. And if you were to just look at the 21st century, the second-lowest BABIP mark since 2000 would be … Estrada's .216, just last year. So it's clear that despite a fastball that rarely touches 90, Estrada has managed to make this into a real, sustainable skill, and that's changed considerably from his days with Washington (.295 BABIP) or Milwaukee (.275).
   To hear Estrada tell it, in addition to adding a cut fastball, the change is mostly from the neck up:
   "My mentality has completely changed the way I go about things [since coming to Toronto]," he said. "I've always worked hard, I still work hard, but in terms of being out on the mound giving up hits and stuff, it just doesn't bother me anymore. I just tell myself I will get the next guy, it's not a big deal, and it's worked."
   It certainly has, and one might assume that pitching in front of a good Toronto defense -- particularly center fielder Kevin Pillar, and pitching to catcher Russell Martin -- has had something to do with it, too. But it's also about forcing the hitter into situations where he isn't likely to succeed. Popups certainly qualify. High-spin fastballs help get you there, and particularly ones with the right spin direction. Estrada's "cue ball" fits the bill.