Analysis of James Paxton’s Return to Seattle
On February 13, the Mariners reached a deal bringing back James Paxton on a one-year deal:
Paxton was traded in the fall of 2018 to the Bronx for prospects Justus Sheffield, Dom Thompson-Williams, and Erik Swanson. Sheffield was consistently in the Mariners’ top 10 prospects rankings until graduating last year, and in 2020 was 25th in fWAR (1.6) among pitchers with at least 50 innings pitched. Since the Mariners have totally rebuilt their farm system, Thompson-Williams and Swanson have fallen out of prospect rankings, but with the level Sheffield is expected to produce in coming years the 2018 trade seems to be a win for the Mariners.
Paxton’s 2020 campaign was his worst season by far. In eight seasons, 2020 was the only time Paxton posted an earned run average (ERA) above 4 and was just the second time he posted a Fielding Independent Pitching (FIP) above 4. However, his 6.64 ERA compared to 4.37 FIP in 2020 may be indicative of inflated numbers due to the small sample size.
Over the last four seasons, Paxton has some numbers that make a one-year “prove it” deal a no-brainer for the Mariners. Since 2017 Paxton is 7th Strikeouts per 9 innings (K/9) among qualified pitchers, and since 2019 is 11th in K/9 among pitchers with at least 150 innings pitched. But can he ride his strikeouts to a bounceback season in 2021?
Our site creator, the talented Max Goldstein (@MaxSportsStudio on Twitter), has created a user-friendly leaderboard of MLB predictive statistics. Access to these leaderboards can be purchased here, and I highly recommend it for anyone who is interested in the objective statistical side of professional baseball. Using this resource, let’s look over how Paxton predicts to perform in 2021. A link to our Advanced Statistics Glossary can be found at the bottom of every article.
Here we look at Strikeout Rate Plus (K%+) compared to predictive ERA (pERA). While Paxton sits in the middle of the pack, he sits above the trendline with some notable company. The players that immediately surround him on the graph are Hyun Jin Ryu, Lance Lynn, and Mike Minor. Ryu’s contract has an AAV of $20M/year, Lynn has an AAV of $10M/year, and Minor has an AAV of $9M/year, so when compared to similar players it seems that Paxton’s one-year deal for $8M-$10M is right on par with market value.
The two biggest concerns the Mariners seem to have about Paxton is injury trouble and if his 2020 numbers were a fluke or actual regression. Paxton’s best season was in 2017 when he posted a 4.4 fWAR in only 136 innings pitched. Two stints on the IL that year would keep Paxton from reaching the qualified numbers of innings pitched. Since his stellar 2017, his expected stats have either regressed to the norm or become outliers.
Looking at Paxton’s expected batting average (xBA), we see that since 2017 Paxton has regressed to the norm and the numbers have plateaued. However, looking at his expected slugging percentage (xSLG) we that 2020 spiked from the plateau of 2018 and 2019:
This increase of xSLG could be due to the fact that Paxton had a career-high home run allowed per 9 innings of 1.77 and a career-high batting average on balls in play (BABIP) of .365 which was .052 points higher than his 2019 BABIP.
Paxton’s inflated 2020 numbers can be attributed to his small sample size, and even if Paxton only provides rotation depth production, his experience should prove invaluable to the younger Mariner pitchers in 2021. Paxton joins a six-man rotation with fellow left-handers Marco Gonzales, Yusei Kikuchi, and Justus Sheffield. While Gonzales and Kikuchi are no spring chickens, Paxton’s knowledge and proven track record should be helpful for Gonzales and Kikuchi should they come to him for advice. And surely the organization is going to be looking for Paxton to mentor the very player he was traded for, Justus Sheffield.
