Despite leading the minor leagues in home runs and RBIs, Peter Alonso didn’t get a callup in September. Instead, Dominic Smith and Jay Bruce got most of the first base reps down the stretch, as Alonso got set to go to the AFL. Predictably, this sent Met fans into a tizzy, prompting many arguments about whether this was the correct move or not.

At its core, the debate here is straightforward. By not calling up Alonso and holding him down for a few weeks in 2019, the Mets will retain control over his age-31 season. More team control is never a bad thing, but it comes at a cost - namely, a lack of data on the viability of Alonso as the starting 1B in 2019. In some ways, it’s a reflection of a philosophical argument that works its way into the discussion of almost every transaction; how important is efficiency for the future relative to doing everything you can to win in the short term? By holding Alonso down, the Mets chose the former.

Here, we attempt to model whether this decision was actually a mistake and, if it was, how costly that mistake was. Ultimately, that’s a question of what’s more valuable - Peter Alonso’s cost-controlled, age-31 season, or information that would help the Mets build a contender in 2019.

We start by making some very simplifying assumptions, while also discussing the limitations of said assumptions:

- To make this analysis easy and discrete (rather than continuous), say there are only two outcomes: Alonso is bad—replacement level or worse—or Alonso is good—2-to-3 fWAR.
- Say that, with no data, Alonso has a 50% chance of being good and a 50% chance of being bad.
- If we saw that Alonso was good in a small sample, say that he has an 80% chance of continuing to be good and a 20% chance of being bad.
- Similarly, if Alonso was bad in a small sample, say that he has an 80% chance of continuing to be bad and a 20% chance of being good.
- Given no data on Alonso, there is a 50% chance the Mets sign a generic first base bat this offseason. This decision would be impossible to project even if we already knew who the GM was going to be, so the best we can do is a coin flip.
- Given data on Alonso, we will assume the Mets follow it. In other words, if Alonso had been called up and was good, we assume the Mets don’t go out and sign another first baseman. Likewise, we assume that if Alonso was bad, the Mets go out and get a first baseman to fill the hole.

Obviously, the correct way to tackle this analysis would be with a flexible projection system where we can add or remove major league stats at will and get a probability density of possible outcomes. Without that, this discrete approximation will work to paint a broad picture.

### Side 1: Control over Peter Alonso’s age-31 season

There’s very little mystery about Alonso’s profile. He’s a mashing, right-handed throwing and hitting first baseman who really can’t play defense. Unless he’s J.D. Martinez with the bat—and it’s unreasonable to project anybody to hit as well as J.D. Martinez—his ceiling is relatively limited. The best results is probably a player similar to the White Sox’s Jose Abreu, who before 2018 consistently posted a wRC+ in the 120-140 range, played terrible defense, and accrued somewhere between 3 and 4 fWAR per season.

That’s a nice player, a solid bat to place in the middle of your lineup, and potentially a Met we could enjoy watching for a half-decade. Unfortunately, arbitration rewards guys who hit home runs and rack up RBIs. If Alonso reached that sort of ceiling for a couple years, he’s likely making $20 million in his final year of arbitration. At a rough valuation of $10 million per win, that means Alonso is providing $10-$15 million in surplus value at 31. This value needs to be roughly halved to account for the time value of money, so this optimistic age-31 season is worth $5-$7 million in present-day dollars.

If Alonso is bad, on the other hand, his age-31 season is worthless. More likely than not, he’s been non-tendered by this point and the Mets are getting no value out of a hypothetical year of control. Based on our assumptions, this has a 50% chance of occurring. As such, we’ll need to halve the value from the optimistic projection, meaning the value of Alonso’s age-31 season is, at best, **$3.5 million** in present day dollars.

### Side 2: Information about the 2019 season

There are two situations where the Mets could have a sub-optimal first base depth chart that hurts the team. We’ll define these two situations as ‘loss states’, with the following associated values:

- The Mets copy-paste Jay Bruce’s contract for [insert generic first base free agent here], but they also have the productive Peter Alonso around. Essentially, $40 million over three years has been thrown away on a limited corner bat that wasn’t needed. We knock $2 million off of that total for each year to account for the time value, giving us a cost of $34 million.
- The Mets rely on Alonso only for him to fall flat on his face. This situation is harder to quantify. What is the “cost” of hurting the team by roughly two wins? A better understanding of the financial values of the playoffs coupled with good projections of postseason probabilities would allow us to quantify this accurately. For now, say that the cost of losing these two wins is exactly that, the cost of two wins. At $10 million per win, that’s $20 million.

But here’s what could have happened if the Mets had called up Peter Alonso for the last month of the 2018 season.

- Alonso is good in 2018 (50%). The Mets choose to rely on him for 2019. If he continues to be good (80%), there is no loss state. If he is instead bad (20%), we reach loss state 2, where the Mets have no productive first baseman.
- Alonso is bad in 2018 (50%). The Mets choose to sign a free agent 1B. If Alonso is actually good in 2019 (20%), we’ve reached loss state 1, where the Mets have an excess at 1B. If Alonso continues to be bad (80%), there is no loss state.

To put a value on this, we simply multiple out the probabilities.

Similarly, here’s what could happen since the Mets didn’t call up Alonso in 2018.

- Alonso is bad in 2019 (50%). If the Mets had the foresight to sign a first baseman (50%), there is no loss state. If the club was relying on Alonso instead (50%), we reach loss state 2.
- Alonso is good in 2019 (50%). If the Mets signed a 1B (50%), we reach loss state 1. If the club was relying on Alonso instead (50%), there is no loss state.

And again, we reach a financial value by multiplying out the probabilities.

Therefore, the rough cost of the lost information is $13.5 - $5.4 = **$8.1 million** in present-day dollars.

### Conclusions

We made some very optimistic projections about Alonso’s future, most notably in his value as a 31-year-old. Despite that, the value of additional information regarding what he could contribute to the 2019 Mets is more than double that of control over his age-31 season. Under this model, the Mets cost themselves **$4.6 million** in present-day dollars.

This analysis did not consider the value of the 40-man roster spot, nor did it factor the potential value of leverage over Alonso if the Mets wanted to extend him down the line, omissions that help Side 1. We’ve also neglected to adequately model the team-building effects of not knowing what Alonso is and how that will change the decisions the Mets’ front office makes as it tries to build a contender for 2019, an omission that would help Side 2.

Regardless, these small chunks of value would likely not close the significant gap between scenarios here. It seems that the Mets’ choice to remain ignorant was indeed a mistake.