The Josh Naylor stat that should have the Mariners sweating his $92.5M contract

For years, the Mariners have had a hard time getting their hands on a solid first baseman. The best offensive season over the past decade with more than 250 plate appearances was Edwin Encarnación in 2019, who posted a 136 wRC+ before he was traded to the Yankees. The only player to have more than 3.0 fWAR in a season was Ty France in 2021. Aside from those two cases, it has been a revolving door of average seasons from the likes of Austin Nola, Daniel Vogelbach, and Danny Valencia.

When Josh Naylor arrived last July and hit to a 137 wRC+ while stealing 19 bases in just 210 plate appearances, many fans felt like the answer to the franchise's issues had finally arrived. The front office seemed to agree, wasting little time in taking him off the board during last year's offseason and making him one of the earliest free agents to sign.

Unfortunately his first full year in the PNW has left quite a bit to be desired. Like his predecessors before him, it has been roughly average, culminating in a 98 wRC+ and just 0.8 fWAR. He does have 29 stolen bases, the most of any first baseman by a comfortable margin, but it's not enough to compensate for the significant dip in production at the plate. Even worse, Seattle may be getting him just in time for a real physical regression.

Josh Naylor's bat speed is already trending in the wrong direction with four more years on his contract

MLB started publishing bat speed data in 2023, at which point Naylor's average speed (MLB only considers a player's top 90% of swings to eliminate outlier data from checked swings) clocked in at 73.2 mph, slightly above average. However since then, it has steadily declined with a sudden drop off between 2024 and 2025.

Bat speed is understandably one of the best intrinsic indicators of physical decline. As players get weaker and older, they swing the bat slower. A lower bat speed typically means fewer hard-hit balls which means less damage and an overall diminished offensive profile.

It doesn't translate perfectly to power production but of all the players who have had at least 400 plate appearances this year, the correlation coefficient between bat speed and ISO is 0.62, indicating a moderately strong relationship.

It's hard to imagine that Naylor's bat speed would take an equally large step forward but it's not out of the question. Jake Bauers, who has suddenly become of the best hitters in baseball, added nearly 3 mph of bat speed from 2024 to 2025. Cam Smith's bat speed jumped from 74.5 mph in his rookie season to 78.0 mph in his sophomore campaign.

At 29 years old, Naylor shouldn't be hitting his physical decline just yet and there could be other explanations for this sudden dip. It's interesting that his two seasons with the lowest bat speed also had the highest chase rates, suggesting that he may have been fully committed to fewer swings upon realizing that pitches were out of the zone.

Another possible hypothesis behind the lowered bat speed is that while bat speed has a positive correlation with ISO, it tends to have a negative correlation with squared up rate and whiff rates. The three lowest average bat speeds belong to Chandler Simpson (65.1), Luis Arraez (63.1), and Steven Kwan (62.4). Of these three, Simpson has the highest whiff rate at 10.7% which is still in the 99th percentile. He also has the lowest squared up rate of the group at 41.8%, also in the 99th percentile.

Naylor's whiff rate of 17.1% is the lowest it has ever been for a full season and his squared-up rate of 32.2% is the highest it has been since Statcast implemented bat tracking statistics. So, there's a chance that this is an intentional change to his approach to be more efficient in his swings and emulate the slap-hitting success of the likes of Kwan and Arraez.

Even if it is intentional, the problem is that Naylor plays first base, not shortstop. Ideally, his role in the lineup is to damage and get runners across home plate. Perhaps this approach would be effective in a world where the Mariners deploy an offensive strategy like that of the Brewers but even Milwaukee's first base tandem of Andrew Vaughn and Jake Bauers prioritize power output over simply putting the ball in play.

As Seattle returns to the drawing board this winter and reassesses what will need to change in 2027, Naylor's approach is one of the individual issues that deserves a closer look. In a best case scenario, this regression in bat speed is intentional and by the start of next year, he can return to being the slugger he was when he first got here in 2025. If not, the Mariners may have to consider cutting bait and trying once again to fill what seems to be a haunted position on the roster.

Add us as a preferred source on Google

Follow