The Oakland A’s have been doing a lot of remarkable things. Whether it’s Matt Chapman‘s otherworldly defensive play at third base, Khris Davis leading the league in home runs, or the phenomenal production of a rotation seemingly cobbled together out of marginal veterans, there’s something to marvel at almost everywhere on the field.

The bullpen is no exception. Led by closer Blake Treinen and his ludicrous triple-digit sinker, the A’s have been unbeatable when they get to the later innings with a lead. That’s not hyperbole: the A’s have won every single one of their 53 games in which they have been ahead at the start of the eighth.

While most teams win when they are ahead at that point, it’s far from a sure thing: MLB teams have collectively won 91.5 percent of games when leading at the start of the eighth. 145 games have been lost from that situation so far this year.

Treinen is a big part of that, of course, but so too is his rookie set-up man, Lou Trivino.Through his first 61 major league innings, Trivino has a 1.62 ERA and 65 strikeouts. While his 3.15 FIP doesn’t quite match that ERA, it is still very good, and a near-identical 3.16 DRA backs up the quality of Trivino’s performance. He also generates ground balls on 47 percent of balls in play.

The 26-year-old is not a household name by any stretch. An eleventh-round pick from Slippery Rock University of Pennsylvania in 2013, Trivino became just the fourth player from that institution to reach the majors when he made his debut early this season. He is the second pitcher, joining Bob Shawkey who, despite the school’s lack of quantity when it comes to major leaguers, has set the bar very high for Slippery Rock alumni with 46.5 WAR and a career ERA+ of 113 over 15 seasons from 1913-27.

Trivino’s standing on prospect lists matched the relative obscurity of his alma mater, which is to say that he didn’t have any. His early seasons as a starter in the minors were underwhelming, even though he was old for the levels. At the start of June 2015, with his ERA at 5.45 for High-A Stockton, Trivino was moved to the bullpen. He has not started a game since.

A move to the bullpen helped Trivino’s stuff to play up, but so did improvements to both his diet and mechanics, as documented by Susan Slusser of the San Francisco Chronicle earlier this year. He compiled a 2.44 ERA across two seasons at Double-A and then a 3.60 mark in the very hitter-friendly Pacific Coast League in 2017. When Trivino opened the season by striking out eight of the first 13 batters he faced at Triple-A this year, Oakland called him up for a couple of games. Although he briefly went back down after that, by April 24th he was in the majors again and has stuck there all season.

Trivino’s background as a starter has left him with a deeper arsenal than many relievers. He uses a curveball as his main breaking pitch but so far that has been featured just 6.6 percent of the time: he now primarily relies on three different fastballs, with a fourseam, sinker, and cutter. It’s the latter that this post will now focus on, as the title indicates.

Many readers will have read that title and immediately thought ‘Mariano Rivera, idiot’. Don’t worry, Rivera is who I thought of too when I first started looking at Trivino’s numbers and noticing that the cutter was pretty handy. Maybe you also thought of Kenley Jansen, another modern example of a prime cutter. I wanted to see how Trivino’s cutter, which appeared to have had excellent results so far, actually stacked up against the best.

That’s only really possible for data since 2007, when Pitchf/x data first became available. Fortunately Brooks Baseball has made that possible for us, with easily-sortable leaderboards for each pitch type. Here’s the leaderboard for all pitchers with at least 200 cutters thrown in the Pitchf/x era. Lou Trivino’s numbers and ranks are as follows:

Batting Average: .125 (1st)

Slugging Percentage: .170 (1st)

True Average: .148 (1st)

Put Away %: 32.65% (1st)

Jansen has a .177 batting average allowed with a .289 SLG and .199 TAv; Rivera, for the years we have data on, is at .196/.280 with a .191 TAv. Other players with far smaller samples come in-between them, mostly of relatively little significance and few get anywhere near Trivino. Based on this data, one could argue that Lou Trivino has the best cutter in baseball.

Trivino has thrown 354 cutters, of which 199 have been swung at, and allowed just 11 hits, with two extra-base hits, one double and one home run. Maybe this still doesn’t sound all that impressive to you, in which case I would first refer you to the ranks above, and then note that we’re not talking about a slider or a curveball which gets employed in two-strike counts the vast majority of the time. Trivino’s cutter is his most frequently-used pitch at over 39 percent and he uses it more often when the batter is ahead or the count is even than when he is ahead.

There’s certainly a small sample size argument to be made here. If we only look at this season, however, Trivino is still first by all measures given above. The closest contender is actually James Paxton, which is more impressive for the fact that Paxton is a starter, and perhaps less so given that he has thrown fewer cutters than Trivino, employing it as the third pitch in his arsenal.

This isn’t really an argument that a rookie with barely sixty innings under his belt genuinely has the best cutter of all time. Jansen has thrown nearly 7500 cutters in our sample, with Rivera at over 4600 plus over a decade more uncounted. There may well be countless other names who never threw a cutter in the pitch-tracking era who had similarly impressive results.

Nonetheless, what is evident so far is that Trivino appears to have one of the most effective cutters we’ve seen in the last decade, at least the first time through the league. Let’s take a look at it in action, against Giants catcher Buster Posey.

The movement and the velocity both deceive Posey. He swings over the top of the ball as it dives late into the very bottom of the zone; if he hadn’t swung, it may well still have been called strike 3. It’s not an incredibly hard pitch, at 91.7 mph, nor does it have a colossal amount of movement, yet it’s more than enough dip to evade Posey’s swing and the velocity is actually key, as we’ll see next. Below is a plot of this eight pitch at-bat from Baseball Prospectus’ matchup visualiser tool.

It’s a fastball-only at-bat, and the key area to look at is the trajectory of pitches 4 and 8. Trivino pumps in that fourseam at 98 mph on pitch 4, which Posey takes for strike two. With two strikes, catcher Josh Phegley keeps trying to get Trivino to make pitch 8, or something like it, calling for the cutter low and on the outer half of the plate. Trivino seems to lose control of the next pitch, a cutter which drifts so far across the zone that it jams Posey’s bat a little on the inside.

6 and 7 are both also big misses, one up that Posey barely pulls foul down the third base line, and the next so low that he does not have to think too hard about swinging. When Trivino gets it right, however, that cutter on pitch 8 looks almost identical to that 98 mph fastball on pitch 4 until very late in its trajectory for a perfect piece of tunnelling, catching Posey both out in front and swinging over the top. It’s even slightly slower than all but one other pitch in the at-bat, with a full tick separating it from pitch 6.

This is a good time as any to note that Trivino’s command is far from impeccable, and he has walked 11 percent of batters faced so far. Striking out Posey is not easy – he has the eleventh-lowest strikeout rate in the majors this year – but it’s also not ideal if it takes four attempts to get the pitch to arrive at a point remotely near where the catcher asked for it.

The at-bat also clearly shows how the cutter can be so effective, and even on the missed spots, like pitch 5, it reveals another key characteristic: the arm-side run. Where the fourseam and sinker move away from righties towards the glove side, the cutter comes back slightly in the other direction:

That run and the late downward movement generate two beneficial outcomes in addition to whiffs: grounders and pop-ups. The cutter has a 45.5 percent groundball rate and 12.7 percent pop-up rate on balls in play. The latter is particularly useful in Oakland, where there is so much foul territory.

Using three fastballs the majority of the time should make it easier for Trivino to repeat his release point than it would be if he was more regularly mixing in breaking and offspeed pitches. A look at the Baseball Prospectus pitch tunnel numbers suggests that is indeed the case. Trivino’s average release points are just 1.58 inches apart, putting him in the 87th percentile in that category, while his ratio between his pitches at the tunnel point (when the batter has to decide when to swing) and the distance apart they are at the plate is in the 94th percentile.

Furthermore, there aren’t too many easy cues for batters in terms of the flight time differential between those fastballs. The fourseam and sinker are essentially the same, sitting 98 and touching 101 at times. The cutter sits at 93 and runs up to 96, making it much harder to tell apart than a changeup or slider might be, at 10-15 mph slower. It serves, in effect, as a very hard changeup, following the trajectory of the other pitches for a long way with slightly reduced velocity and late break downwards.

A look at some Statcast-based charts, courtesy of Baseball Savant, further elucidate the extent of Trivino’s success at limiting good contact. First, here are all the balls in play against Trivino, broken down by exit velocity and launch angle:

While Trivino has probably been a little fortunate on balls in play, his expected wOBA against the cutter is still an elite .208. Worse than his actual .163 mark, to be sure, but a massive amount better than the league-average of .324. There has only really been one truly crushed ball hit against Trivino: the home run he has given up, hit by Justin Upton, represented by that green dot in the ‘Barrels’ section of the image. That was a first-pitch blast on another huge missed spot, as can be seen below:

It’s hard to effectively tunnel when the batter doesn’t see more than one pitch. Again, we see how Trivino can lose the feel of the cutter and essentially serve up a 92 mph meatball. Upton represents the exception rather than the rule, of course. The spray chart below shows how rarely hitters have managed to hit the ball deep against the A’s reliever.

That’s a whole lot of grounders, easy flies, and nothing in the way of outfielders having to run back to make a play on the warning track. Chapman hoovering up everything on the left side of the infield certainly helps, of course.

If this look at Trivino’s cutter has taught us anything, it’s that it can be devastating when he gets it right, and yet it can go wrong rather more often than the initial numbers suggested. That’s been the worrying recent trend in August, which has seen Trivino go to the sinker far more often than the fourseam and seemingly lose a bit of movement on the cutter too. The sinker is less separated from the cutter in terms of vertical movement, and the pitches are getting closer together:

That trend has produced some worrying results. Trivino has five walks and just six strikeouts in August, with opponents hitting .290 against him. Here’s Trivino’s heatmap on the cutter from April through the end of July:

And here’s how it has looked in August:

There’s evidence of the pitch staying up and leaking back out over the middle of the plate more often, like that Upton home run, and even further over to the arm side. More are missing outside the zone too, making it easier for opponents to lay off those pitches than it was earlier in the year. Trivino is getting far fewer whiffs on both the fourseam and the cutter this month, so it’s no surprise the overall strikeout rate has dipped.

It’s possible that opponents are simply finding it easier to hit Trivino now that teams have seen his arsenal a decent amount, and without significant breaking or offspeed pitch usage it’s easy for them to sit fastball. The wavering control also suggests a mechanical issue, though, and at 6’5″ Trivino would hardly be the first tall pitcher to struggle with keeping his action consistent, or the first rookie to suffer from fatigue late in their debut season. If he can repeat the cutter more effectively along with the other fastballs, maintaining that excellent tunnelling we’ve seen at times, it still seems like Trivino has the components for success.

So Lou Trivino may well have had the best cutter in baseball at one point this season. It doesn’t seem like he has it right now. That’s a testament to how quickly major league hitters can catch on, how difficult it is to maintain such a high level over a full season, and how fleeting success can be. Hopefully Trivino can rediscover the form that made him so effective early in the season and help the A’s to the playoffs. As for the cutter, he might have a little way to go before he can truly top Jansen and Rivera.