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Analyzing the Return from the Tyler O’Neill Trade

The Cardinals received promising bullpen help and upper level rotation depth.

MLB: Boston Red Sox at Toronto Blue Jays Dan Hamilton-USA TODAY Sports

Your opinion of the Tyler O’Neill trade probably correlates with your level of expectation about a trade which has been inevitable for a little while now. Personally, I wasn’t expecting much of a return for an oft-injured player worth 2 fWAR in the past 2 seasons combined.

Sure, O’Neill has upside - he showed it in 2021 - but that upside isn’t enough to overcome the injury issues and the inconsistency he showed when he was on the field. So that means the headliner of the package coming back to the St. Louis Cardinals is an unproven major league reliever.

You can be disappointed by that if you want but Nick Robertson is a legitimately interesting pre-arb bullpen arm with plenty of upside. The other player coming back is Victor Santos who I don’t rate as highly but still provides useful upper level rotation depth.

Let’s dive into the headliner first.

Nick Robertson

The most exciting thing about Nick Robertson is his new and completely nasty sweeper. But because that’s his newest pitch and I have a lot more to say about it, I want to start with a discussion of the rest of Robertson’s arsenal to help show why the sweeper fits in so well.

And I’ll start with the fastball.

The pitch averaged 95.3 mph in 2023 with 16.3 inches of induced vertical break (the league average IVB on four-seamers in 15.7 inches) and 7.6 inches of run. That’s a mediocre fastball shape, which normally wouldn’t make me too excited about it. But there’s another consideration too. Robertson has elite extension.

The righty averages 7.1 feet of extension, which puts him among the top 5% of all MLB pitchers. It also means that his pitches look faster than they are. Perceived velocity tells us this and Robertson’s perceived velocity is 96.8 mph, 1.5 mph faster than his actual velocity.

That helps the pitch play up a bit. It’s still not an elite offering by any means but it gets on hitters quickly and that helps it overcome it’s pedestrian shape.

The go-to secondary pitch in Robertson’s arsenal (at least prior to September) is a changeup that profiles well and was consistently considered his best pitch throughout his minor league ascent.

It only gets about 7 mph of velocity separation from Robertson’s fastball but that’s okay because the pitch gets a ton of vertical separation (17 inches) and horizontal separation (8.3 inches). Normally I would look for a changeup with a velocity difference in the 8-12 mph range but if a pitcher can get enough of a movement difference from the fastball, it makes it less important for him to be in that range.

So Robertson’s changeup is a bit of a firm dropper (not technically though because firm droppers tend to have even less of a velocity difference) and firm droppers tend to play well.

If Robertson’s arsenal just contained those two pitches, it would be fine. Nothing special but just fine. The third pitch in Robertson’s arsenal - a slider - is really the key.

According to this excellent article from Quinn Riley, Robertson’s third pitch used to be a slider that got about 5 inches of sweep and was used around 10% of the time. That’s pretty traditional slider movement, with maybe a bit more sweep than the average slider, but it was a clear third pitch for him.

That all changed when he developed his sweeper this year. And it’s nasty. Like this nasty:

That looks like a wiffle ball. This is the kind of addition that really takes a pitcher’s arsenal to the next level. And the interesting thing is that he really started to utilize the pitch in the final month of the season. Before September, the pitch was used less than 10% of the time. Then September rolled around and he jacked up his sweeper usage to 36.4%.

There are so many things I love about this graph that I don’t even know where to begin. This is what it looks like for a pitcher to optimize his pitch usage.

For starters, I love that he started throwing more sweepers (classified as a slider on Baseball Savant). The pitch simply has a nasty profile and deserves heavy usage, specifically against right-handed hitters.

It averages 83.3 mph with 14.6 inches of sweep and 36.4 inches of depth. That’s a true monster and, as a result, the pitch had a 147 stuff+ grade in 2023. I’m on team throw-your-best-pitches-more so I fully support the change that Robertson made with his pitch usage in September.

The pitch that took most of the hit was Robertson’s changeup and that’s okay for the most part. I don’t dislike the pitch. In fact, I think it’s a good offering. So why do I think it’s good that Robertson is throwing it less?

Because it means he stopped throwing same sided changeups. I’m not opposed to same sided changeup as a general principle. They are a good strategy for the right pitcher. But for a pitcher with a nasty breaking ball, there’s no point to throwing same sided changeups.

Sweepers tend to have heavy platoon splits while changeups tend to play better against opposite handed hitters. So, pitchers with nasty breaking balls should never favor their changeup over their breaking ball when a same sided hitter steps into the box.

So, taking a look at Robertson’s pitch usage against righties, we can see that he basically stopped throwing his changeup, decreasing it’s usage to a measly 1.4% (he threw 1 R/R changeup in September).

There are few things that get me excited more than pitchers optimizing their arsenals, so, obviously, I’m a big fan of this. Another thing I want to point out is that the sweeper actually became Robertson’s primary pitch against righties in the final month of the season.

I love that and I hope it continues.

Robertson didn’t just tweak his breaking ball and his pitch usage, though. He also tweaked his horizontal release point.

Now, you might think this means that he lowered his arm slot but that’s not actually the case. Well...not entirely. He did indeed lower his arm slot during the season but it was only a slight change. That change also occurred in August and not September so it’s not the reason why Robertson’s horizontal release point changed.

That change is because Robertson moved on the rubber. He used to throw from the first base side of the rubber and in September he started throwing from the third base side.

This might not seem like it matters all that much but it does.

This has everything to do with something called horizontal approach angle, the lesser known cousin of vertical approach angle.

So what is horizontal approach angle (HAA)? It’s the angle at which a pitch enters the zone horizontally. Pretty straightforward, right?

So by moving to the first base side of the rubber, Robertson’s arm is releasing the pitch well off the plate and creating a sharper inward angle toward the plate. This is a good thing because research tells us that sharper HAAs lead to better pitch performance, specifically in same handed matchups.

(The tweet is specifically focused on breaking balls but there are 6 tables in it that cover breaking balls, fastballs, and changeups so check it out if you want the data on all pitch types.)

So by shifting where he stands on the rubber, Robertson is making a simple and subtle tweak in an effort to miss more bats. That’s not something that should be overlooked.

The results haven’t been there yet for Robertson but his underlying metrics tell a much more positive story. He’s a pitcher that I’m 100% willing to bet on because he has nasty stuff and took big steps in September to optimize his arsenal. The guy has true bat-missing potential and that could add another weapon to the Cardinals bullpen.

He’s also a pre-arb reliever so he’ll be relatively cheap and controllable for a while. It may not be too exciting to see a reliever with a 6.04 ERA headlining the return for Tyler O’Neill but Robertson’s true talent is much better than his inflated small sample ERA. His FIP and xFIP tell a different story and so do his pitch metrics.

Victor Santos

The other player coming back to the Cardinals is 23 year-old Victor Santos, who reached Triple-A and held his own at just 21 years old.

He’s not a guy with big stuff but he does know how to throw strikes and command his arsenal. He also knows how to mix his pitches, which is something that I find appealing.

Interestingly, Santos has relatively wild mechanics with a long arm, an inward leg lift, and some effort in the delivery. That’s not something I expected from an arm with such a long history of plus control but the righty does seem to repeat his delivery well which helps.

The guy loves to throw sliders and changeups and isn’t a fastball heavy arm at all. That’s a good thing because he’s not overpowering from a pure stuff perspective. Most scouting reports have Santos throwing a sinker as his primary fastball but it appears to be a sinker that doesn’t have a ton of depth.

It gets some arm side run and appears to have more riding life than the average sinker so I would actually be curious to see how effective the pitch would be at the top of the zone considering Santos generally likes to keep the pitch down. Still, he commands the offering pretty well and is able to work it effectively to both sides of the plate.

It only sits in the low 90s so it’s pretty clearly a below average pitch and he likes to use it off of his slider and changeup and not the other way around, which does help him hide it a bit.

The slider gets good two plane movement with some sweep and good depth. It’s fine pitch but I actually prefer Santos’ changeup which he commands better and shows great fading life. Baseball America tagged it as his best swing and miss offering in 2022 so that’s also a plus. It looks like a split-change to me but it’s hard to see the grip out of his hand so I can’t be certain.

Overall, the arsenal is fine but it is interesting to see that Santos’ strikeout rate saw a jump in Triple-A. I haven’t had enough time to really examine what changed for him, if anything, but I will say that his secondaries look good enough to miss a decent amount of bats and, considering how much Santos uses them, I wouldn’t be shocked if he was able to maintain a strikeout rate somewhere in that 20-25% range.

Obviously that’s not super high but it’s playable for a depth starter with excellent control.

Looking past the arsenal, Santos loved to pitch quickly in 2022, to the point of making hitters uncomfortable. He also seemed to occasionally have bouts of wildness where he would lose his command before finding it again and I do think it would help him to slow down a bit in those instances.

Something else worth pointing out is that since he missed the entire 2023 season, we have yet to see what kind of effect the pitch clock will have on his tendency to work quickly. I’m guessing that it will neutralize that advantage for Santos much like it did the same to Zane Mills who also was able to make hitters uncomfortable with his pace prior to the pitch clock era.

Keep in mind that because of Santos’ injury (likely TJS but I can’t find any hard information on the injury) which kept him out for all 0f 2023, this scouting report is a bit dated. The righty has been pitching in the Dominican Winter League this year, and has been pitching well, but I haven’t been able to see him at all yet.

While pitching for Leones del Escogido, he has a 2.96 ERA paired with a 19.8% strikeout rate, a 5.2% walk rate, and 0.3 home runs allowed per 9 innings. LIDOM is generally a league that favors pitchers so that should be factored in but those are still good numbers and that’s an encouraging sign for a pitcher seeing his first game action in 2023.

I’ll have to try and catch his next start if possible.

Overall, Santos may not be the most exciting arm but he is interesting and should provide the Cardinals with more upper level rotation depth, which is something the organization has really built up via trade in the last few months.

I’m excited to see Santos get back on the mound in affiliated ball in 2024.


This wasn’t a bad return for Tyler O’Neill. In fact, I actually like it but I will admit that my expectations for O’Neill’s value were pretty low.

The Cardinals snagging an interesting pre-arn reliever with a ton of bat missing upside who optimized quite a few things in the final month of the season is exciting. Santos may be less exciting but upper level rotation depth is always valuable and anyone who can hold his own in Triple-A as a 21-year-old is worth keeping an eye on.

This is a solid package of players that can help the Cardinals in 2024 and I would expect Robertson to hold down a bullpen spot for a decent chuck of the year even if he doesn’t make the Opening Day roster.

Another impact of this trade is that we now know what comes next for the Cardinals. They may still make a trade for another starter since they just freed up a projected $5 million by trading O’Neill but they also need to sign free agent relievers and I would expect to see them move fairly quickly to do so.

Thanks for reading, VEB. Have a great Sunday!