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Why Nick Nelson?

What, an 8.79 ERA isn’t good enough for you?

New York Yankees v Seattle Mariners Photo by Steph Chambers/Getty Images

Prior to the lockout, teams were making moves left and right. It was a lot of the usual stuff where teams were getting their 40-man rosters ready for the Rule 5 draft, but once the transaction freeze hit, that planning was set aside for the time. The Phillies were no strangers to these moves, making moves that would net them some catching depth that they badly needed in the upper minors, but also had them acquire a pitcher that had an 8.79 ERA in 2021. Needless to say, there was an eyebrow raised about this acquisition, but with the introduction of some new stats into the sabermetric arena, maybe the move makes a little more sense after all.

By this point, you may recall the team making a trade with the Yankees where they got Nick Nelson on the cheap. Nelson had pitched himself out of the favors of the team in the Bronx and the Phillies, in need of some cheap depth for their ever inflamed bullpen, were ready and willing to get him. It was a move that was reminiscent of their trading for Sam Coonrod prior to 2021, a trade that saw them give up a prospect that some thought had a real future, but ultimately, the Coonrod trade was a success. He gave the Phillies 42 13 innings of solid, dependable relief work, striking out 25.9% of batters he saw and lowering his walk rate from 9.9% to a more palatable 8.1%. The team recognized something in him that they thought they could fix, made the adjustment and got good relief work. They’re hoping to turn the same trick with Nelson this year. The only thing that is hard to understand is what they could see in Nelson that the Yankees, a pretty analytically inclined team, no longer wanted any part of? A few clues could be in using a new stat that is becoming en vogue around front offices, as well as encouraging some more use of the repertoire.

Here is where we talk about one of the newer stats to come into play: VAA, or vertical approach angle. In basic terms, VAA is the angle at which a pitch crosses home plate. There are many articles out there that can help you understand this, so rather than bore you to tears with all of the information, we’ll link them here. The first one might be this video that gives it to you pretty simply, followed by this one from Alex Chamberlain at Fangraphs and this other one from Iowa Baseball Managers. Give both of them a read before continuing here.

Ready? Ok.

There could be something with Nelson and his own VAA that the Phillies think they might be able to fix. First, some data.

In 2021, Nelson was fixated on throwing his fastball, throwing the pitch 53.8% of the time. He vacillated between that and his changeup, the two accounting for near 88% of the pitches he threw. The issue is that his fastball got, in the words of Ben Davis, “K-I-L-T KILT!” to the tune of a .750 slugging percentage by opposing hitters off of it. 2020 wasn’t much better (.629 SLG against the fastball), but that much of a jump is a cause for concern, especially when Nelson possesses the arm to be able to live in 96-98 mile an hour band. The issue comes to how he was using the fastball ineffectively, not pitching to his strengths and to his VAA.

In the linked video and articles, the basic premise is that those with a “flatter” VAA, in the 0 to negative 4 degree range, should be living somewhere at the top of the zone. Those with a “steeper” VAA should be somewhere towards the bottom. As Zahradnik talks about in his article, whiff rate on the fastball climbs at the top of the zone as the pitch’s VAA approaches 0. The opposite is true as the pitch moves away from 0 at the bottom of the zone. I’d encourage you to go back and look at the data again, but Zahradnik explains it well:

It’s pretty simple: if the fastball VAA is flatter, the primary location should be high in the zone. If the pitch has a steeper VAA, it should be located lower in the zone more often than not.

Using this explanation, we can start to look at what went wrong for Nelson in 2021. Here is a graph that shows where he was throwing his fastball last year.

Compare that with where he was throwing the pitch in 2020, when he wasn’t good, but still had better numbers than in 2021.

2020 saw him throwing the pitch higher in the zone than he did in 2021. Was he following what he should have been doing? That’s where we go to another data set.

Using Chamberlain’s own running record of all sorts of information on pitch data, we can ascertain what Nelson’s VAA is on his fastball both last year and in 2020.

Nelson VAA fastball

Year VAA Ext (ft.)
Year VAA Ext (ft.)
2021 -4.6* 6.4
2020 -4.4* 6.4

The difference on the VAA in his fastball is almost negligible, yet as we saw in the usage maps, he attacked different parts of the strikezone last year. So why did he change where he was throwing it? The change in pitch location could be one of the reasons he struggled so much with the fastball last year and why he was getting torched with regularity. Could it be that his command with the pitch wasn’t good enough to allow him to consistently stay at the top of the zone with the pitch? It’s possible. After all, Coonrod wasn’t exactly a paragon of command himself prior to coming to Philadelphia, but working with the pitching coaches obviously helped him establish the pitch as an upper echelon pitch among relievers.

Circling back to the question of why did the Phillies trade for Nelson, it’s possible that they saw this information for themselves (on a more granular level) and thought they might be able to tweak his pitch selection and be able to get some better results from him. It isn’t a guarantee that they will, but using what we know about VAA, the team might be trying to get him to live more in the top of the zone to make his fastball a more effective pitch. When he did throw it at the top last year, he was getting whiffs with it, at times, better than league average.

They’ll have to teach him some command with the fastball, but as the evidence shows with Coonrod, it’s something that they have demonstrated they are able to do.

If we’re looking for other reasons why the team traded for Nick Nelson, we can also look at a way for the team to tweak his pitch usage. I showed earlier that Nelson relied on either his fastball or changeup nearly 88% of the time in 2021. Rendering a pitcher as a two pitch pitcher isn’t a bad idea, but when the two pitches are so similar and the pitcher lacks anything that moves horizontally, it can only help the hitter focus on certain areas of the strike zone. Nelson’s changeup moves, but it’s still not something that will threaten a left-handed hitter.

That means he’s got to come up with another pitch if he wants to find some success. Luckily, looking at his 2020 season, there is evidence that his slider can be used if used correctly.


Year Usage Horiz. movement (in.) Vert. movement (in.) BA/SLG
Year Usage Horiz. movement (in.) Vert. movement (in.) BA/SLG
2020 12.3% 11.2 41.9 .267/.267
2021 8.3% 9.3 38.5 .143/.143

Are there extremely small sample sizes? Of course, but without the pitcher using an effective pitch more often, it’s tough to say that he might have done better. The evidence is there that he might have, but we’ll never know.

Listen, signing Nick Nelson isn’t going to move mountains. He’s got some minor league options left, has pitched at the major league level (albeit ineffectively) and can ride the shuttle with no issues. But if the team can get him to attack the strike zone in better places, if they can convince him to throw one of his breaking pitches more often, if they can coax a little Coonrod-esque revival out of him, they will have set themselves up nicely with a cheap bullpen option that they can discard at the first sign of trouble. No harm, no foul. We’ll just have to see if Nelson can adjust.