For nearly 15 years, and now close to 600 saves -- 595, seven from setting the all-time record, entering Friday -- Rivera has thrown mainly the same pitch, time after time. Nearly every time, hitters know it's coming. And the vast majority of the time, even against hitters who have seen him for years, he gets the same result. It might be one of the most predictable results in baseball over theplast generation, and it's still entertaining to watch.
"I'd have to say," Tigers manager Jim Leyland said, "that he's the greatest closer of all time."
Rivera didn't invent the cut fastball, but he just about perfected it.
The cutter was around for years before Rivera, even if it didn't go by that name, and had its share of proponents. But with Rivera, it has its face, one whose performance has inspired many pitchers to pick up the same pitch. For the vast majority of them, it's a complement to other pitches they've thrown their whole careers. For Rivera, it has been his career.
No single pitch, not even Trevor Hoffman's changeup, has meant as much for such a great pitcher as the cutter has for Rivera.
"To be able to be as effective as he has with just primarily one pitch," Rays manager Joe Maddon said, "it's probably the only time it's ever been done. His cutter has been incredible."
From a mechanical standpoint, the grip is just a little different than a regular fastball. If it's done right, the hitter sees something vastly different, and he doesn't see it until he's already had to react.
Some pitchers, like National League Cy Young Award winner Roy Halladay, learned it from a pitching coach and ran with it. Rivera's cutter came by accident. But once he worked on it, he made a science out of it. And no matter how many try, nobody can quite duplicate it, for multiple reasons.
One big reason, Tigers veteran Brandon Inge said, is the difficulty in reading it.
"There are other people that throw cutters out there," Inge said, "but you can see the spin on the other guys' cutters. You cannot see the spin on his. His looks like a four-seam fastball every time he throws it. When he was in his prime, he was throwing it like 96 mph."
Rivera doesn't throw it that hard now. According to fangraphs.com, Rivera's cutter this year averages 91.3 mph, and that's up slightly from last year. The important part, though, is that it comes in at nearly the same speed as his normal fastball.
Until the very last moment, too, it moves like a fastball. Then, it breaks late. And when it does, it breaks hard toward the first-base side of the plate. For a left-handed hitter, it's breaking in on his hands. For a right-handed hitter, it's breaking away.
Inge compared it to a pitch a kid would come up with using a Wiffle ball.
"I kind of had it down to a science," Inge said, "that if the ball started in one area, when it moves, it would be about a foot away from that area. That's where the ball was going to end up."
That doesn't mean he could hit it. Inge is 2-for-12 lifetime off Rivera, with one strikeout. Others have fared worse.
Even those with success off Rivera marvel at the pitch. No active player with at least 10 plate appearances off Rivera has hit him for as good of an average as Magglio Ordonez, who is 7-for-14 (.500) against him. But as Ordonez explained, that's because he's trained to hit pitches to the opposite field. A cutter breaking away from him plays right into his swing.
"You see it, and it's breaking late," Ordonez said. "When you've got to swing, it breaks. It's not easy."
The only other pitcher Ordonez sees who throws the cutter as such a big out pitch is the Angels' Dan Haren. But Haren doesn't throw it as hard or mask it with a similar-looking fastball.
Unlike other cutters, Rivera's cutter doesn't break down much, if at all.
"And that's why he's so effective," Inge said. "It doesn't drop. It almost looks like it rises. It keeps the same plane. It just goes across. It doesn't go down, like most people's cutters and sliders do."
Maddon sees another unique characteristic of Rivera's cutter, before he even releases the ball.
"I think the mechanics of it are what makes it different," he said. "He throws it from such a high arm angle, and that's really where the effectiveness is created. If he was more of a three-quarter [arm angle] pitcher, I don't think it would've been as effective as it has been, because he comes right over the top pretty much.
"I think for that reason, and the way it breaks because of that, has made it good to both righties and lefties for as long as it has been."
Rivera throws it the same way, time after time, and makes it break consistently, right where he wants it.
One of the best recent developments in pitching-trait analysis is the Pitch f/x data that comes out of MLB.com's Gameday application and other services. It can measure how far a pitch breaks -- where a pitch lands in relation to a strike zone -- and graph it. It shows Rivera's cutter moves a little vertically and a lot more horizontally. And it shows up time after time around the same spots -- inside corner for left-handed hitters, at or off the outside corner for righties, with the occasional pitch in on a righty after seemingly heading toward him.
Foster that consistently nasty pitch, an inning or two at a time, and Rivera hasn't needed much variety.
Every year since 2004, the second year STATS Inc. began tracking pitch types, the cutter has accounted for at least 80 percent of Rivera's pitches. This year, even though hitters have noted a sinker mixed in to jam right-handed hitters, he's throwing cutters on nine out of every 10 pitches.
Rivera's approach to right-handed hitters uses the cutter as his workhorse pitch and mixes in his fastball for show, almost the opposite of most big league pitchers.
To left-handed batters, it's even worse. According to STATS, as of the start of this week Rivera had yet to throw anything other than a cutter to a left-handed hitter this season. Last year, he threw just two non-cutters out of 434 pitches to lefties. Two years ago, it was four out of 510.
So far this year, according to STATS, opponents are batting .229 against Rivera's cutter. Compared with most years, that's high, except for a .245 average in 2007. Yet, hitters are swinging and missing at nearly 20 percent of his cutters, even though better than half of them are in the strike zone.
Those who suggest Rivera's cutter is losing its effectiveness are judging by his high standards. They've certainly seen enough of them to judge.
"Everybody's known it's going to break for the last, what, 15 years?" Maddon said, "And they still can't do anything with it."