Now, let’s compare each as a hitter. Below is each player’s wRC+/OPS+/DRC+ splits by season:
This puts Donaldson’s average splits at 139/137/132 while Arenado’s sit at 129/130/135. If you exclude Donaldson’s injury-riddled 2018, he’s at 147/143/141. If we expect regression from Donaldson due to age, as we should, that would mean we’re still likely to see him put up similar production to what Arenado’s done in the lineup the past few seasons in terms of wRC+/OPS+/DRC+.
Now let’s take a look at how each player has gotten to those numbers.
Arenado ended 2019 with a BB% of 9.4% and a K% of 14.0%. These are in line with his career average numbers and they read similarly in 2016 and 2017 (2018 was higher in both BB% and K% but not tremendously off).
Donaldson ended 2019 with a BB% of 15.2% and a K% of 23.5%. Those are also fairly in line with his recent history so we shouldn’t expect much change from those numbers for either Arenado or Donaldson.
As for how each player is hitting the ball, here’s how they’ve trended. Arenado’s Hard Hit% from 2016 to 2019 was 37.9%, 36.7%, 42.9% to 42.1%. It’s reasonable to expect he’ll be around 42% again this season. He also has been consistent on his Line Drive/Groundball/Flyball splits, posting up a line of 19.3%/36.0%/44.7% in 2019 with a HR/FB% of 18.2% (slightly above his career average).
Donaldson appears to have found something in his swing in 2019 that’s causing him to hit the ball hard. His Hard Hit% from 2016 to 2019 was 40.4%, 36.3%, 41.0% to 47.5%. Assuming a similar swing this season, it’s reasonable to expect a Hard Hit% around 45%. His LD%/GB%/FB% in 2019 was pretty close to his career averages as well sitting at 21.5%/42.2%/36.4%.
Where Donaldson really starts to distance himself is how often he barrels the ball. According to Statcast, in 2019 Donaldson averaged a Barrel per PA of 9.4%. That ranked 17th overall in the majors. Arenado’s Barrel per PA% sat at 6.0%, which ranks 146th. In terms of Expected Stats, Donaldson’s xwOBA in 2019 was .387, good enough for 19th in the majors. Arenado’s was .344, ranking him 101st.
With Donaldson trending in the right direction in terms of expected stats, while still putting up very solid numbers in his park factored stats, he’d actually be a small improvement to the lineup in a holistic perspective if he were to replace Arenado. At the very least, we could expect similar production to what we’re currently getting from Arenado, just on a shorter timeline given Donaldson’s age.