New York Mets first baseman Pete Alonso have proven quite a bit during his incredible rookie season, but one thing that stands out the most is his propensity for hitting home runs. After all, the dude has slugged 47 dingers so far this season, has already set the Mets rookie and franchise record, the National League rookie record, and is bearing down on Aaron Judge‘s MLB rookie record of 52.
Alonso’s first half of play was eye-opening in its own right, as the 24-year-old collected 30 homers and 68 RBI with a 1.006 OPS, .354 ISO, and 158 wRC+. As opposing pitchers have tried adjusting to him, his statistics have normalized a smidge since the All-Star break, but he’s still punishing baseballs frequently. Through 208 plate appearances, he’s slugged another 17 homers with 41 RBI, which has led to a .860 OPS, .272 ISO, and 123 wRC+.
Even with the adjustment period from the first half to the second half, Alonso has found ways to keep his production at an above-average level. One of the things he’s changed over the course of 2019 has been his aggressiveness in the strike zone. Alonso’s swing rate has increased a few percentage points between these two periods of time, and it’s mostly because he’s swinging more often at strikes.
Prior to the All-Star break, his swing rate on strikes sat at 64.4%. That number has increased to 73.3% since the midsummer respite, and while it hasn’t been accompanied with a similar increase in contact rate (84.2% to 82.8%), this is at least a sound approach to have moving forward.
When comparing Alonso’s numbers from the first and second half, something that caught my eye was a drop in curveball usage from opposing pitchers (14.0% to 10.8%). This was interesting because when looking at his pitch-by-pitch splits, it was the only offering he’s seen 100-plus times where he hasn’t produced a wRC+ higher than 140 (it’s currently at 73). That overall lack of production compared to the other pitches he’s faced hasn’t put a damper on his curveball-specific ISO, which currently sits at .283.
All of that led to me wondering how exactly the rookie’s homer distribution has looked throughout this season. And as it turns out, it doesn’t really matter what pitch is thrown his way — Alonso has a good chance of doing extreme damage with it. The following table shows how his homers and ISO are distributed among pitches he’s seen at least 100 times so far this year.
| Pitch | # of Homers | ISO |
|---|---|---|
| Four-seamer | 20 | .456 |
| Sinker | 7 | .232 |
| Slider | 5 | .253 |
| Curveball | 5 | .283 |
| Changeup | 8 | .387 |
| Cutter | 2 | .292 |
This is what you call spreading the love, and it also speaks to Alonso’s skill of being a pure hitter and more than just a one-dimensional slugger. His performance on four-seamers jumps out here for obvious reasons. It’s the pitch he’s seen the most as a rookie, yet his ISO is still head-and-shoulders above any other offering.
And you know what’s even more interesting? The frequency in which he’s seen all types of fastballs has actually increased from 50.9% prior to the All-Star break to 54.3% following the midsummer classic. As things have changed against him, Alonso has found a way to remain productive on a daily basis. He hasn’t posted a month with a wRC+ below 103 yet this season, and based on how his September is going, that trend is unlikely to change in the regular season’s final month.
Alonso has outperformed any and all expectations people may have had for him heading into 2019. Even when I took a look at how he could potentially compare to other great rookie seasons for Mets position players prior to Opening Day, he blows them out of the water in virtually every metric, and then some. It’s been a pleasure watching him punish baseballs on a nightly basis, and more importantly, New York now has an elite anchor for its lineup in the same way the rotation has an elite anchor in Jacob deGrom for the starting rotation.
