Taking a look at whether or not there is any reason to think that the Red Sox roster might support Perez better than Minnesota's did last year, I took a look at Perez's GB/FB ratios and 2019 splits, and the Twins' defense in the relevant section of the field (IF or OF, depending on Perez's GB/FB ratio).
For Perez, starting with his splits, Perez was both worse at home (809 OPS against vs 753 on the road), and was far worse in the second half of the season (678 OPS against 1st half, 917 in the 2nd half!). Interestingly, Perez went from being a bit of a GB pitcher in 2014-2016 (GB/FB ratios of 1.11, 1.50, and 1.15) to more FB-oriented in 2017-2019 (0.90, 1.06, 0.95). Obviously's Perez's injury history and resulting lack of IP in several seasons injects large error bars into this information, but this could be an indicator that Perez has made a similar adjustment to Porcello's - to be more of a K/FB pitcher than a GB pitcher, given the recent launch angle revolution. Whether those results are random or the result of a deliberate approach by Perez, it stands to reason that he might be impacted (for better or for worse) by the quality of the OF defense playing behind him.
This discovery excited me for a brief moment, before I remembered just how awful the Red Sox were at converting balls in play into outs in 2019 (DefEff of .673, well below the LgAvg of .688, and tied for 4th worst in all of MLB). In a previous thread during the 2019 season, I had already picked at the scab that was the 2019 Red Sox OF defense, and its decline from its 2018 excellence. The one piece of good news is this - the team that the Red Sox were tied with for the 4th worst Defensive Efficiency in MLB was the Twins.
So, is there any actual indication that the Red Sox OF defense could be an improvement over Perez's 2019 situation? As it turns out...maybe. Let's start by looking at the Twins' OF defense. I'm starting with B-ref's total zone, because their website is handy for figuring out who played which positions, before I look at Fangraphs data.
Unlike the 2019 Red Sox, who were relatively stable across the 3 starting OF spots with Beni, Bradley, and Betts, the Twins' situation was more complicated. Although Eddie Rosario held down LF (124 G), CF saw 3 different starters across Byron Buxton (86 G), Max Kepler (60 G), and Jake Cave (23 G), while RF also 3 different starters between Kepler (84 G), Cave (45 G), and Marwin Gonzalez (44 G).
The following table for the 2019 Twins OFers contains the following stats from B-ref and Fangraphs: Total Zone Fielding Runs Above Average (Rtot), BIS Defensive Runs Saved Above Average (Rdrs), and The Three Components of UZR (ARM, RngR, and ErrR).
Position |
Player |
Rtot |
Rdrs |
ARM |
RngR |
ErrR |
LF |
Rosario |
-8 |
-6 |
2.1 |
-7.4 |
-0.4 |
CF |
Buxton |
7 |
10 |
3.2 |
5.6 |
-0.1 |
CF |
Kepler |
-2 |
3 |
-1.3 |
3.5 |
0.6 |
CF |
Cave |
-3 |
-3 |
-0.9 |
-1.6 |
0.2 |
RF |
Kepler |
13 |
4 |
2.0 |
6.8 |
1.0 |
RF |
Cave |
2 |
-1 |
-2.1 |
1.3 |
-0.4 |
RF |
Gonzalez |
-1 |
2 |
-1.5 |
0.4 |
-0.7 |
Yes, I know we're dealing with small sample sizes of defensive stats here. I'm merely trying to review what happened in the past, not projecting the actual future performance of these players, or trying to ascertain their true talent levels. What appears to have happened is that the Twins had an adequate OF defense with their Opening Day lineup of Buxton in CF (Good), Kepler in RF (Good), and Rosario in LF (Bad). Once Buxton got injured, the updated configuration of Kepler in CF (Mediocre) or Cave in CF (Bad), Cave in RF (Mediocre) or Gonzalez in RF (Mediocre), and Rosario in LF (Bad) was not going to do a pitcher with Perez's GB/FB ratio any favors. Another item worth noting is how Perez's 1st and 2nd half splits coincide with Buxton's games played - Buxton played a total of 73 games in the 1st half (Perez 678 OPS against, .303 BABIP), but only 14 games in the second half of the season (Perez 917 OPS against, .336 BABIP). I wouldn't go so far as to blame Buxton's absence, and the subsequent downgrading of the Twins' OF defense for Perez's 2nd half collapse, but I think it's also reasonable to suggest that there is something here beyond the level of coincidence.
Here's what the 2019 Red Sox OFers did for comparison's sake. I'm including each player's 2018 numbers in parentheses for the sake of highlighting the 2018 -> 2019 defensive collapse of the group.
So, for whatever reason, it appears that both Beni and JBJ fell off some kind of defensive cliff in 2019, regardless of which defensive metrics you prefer. We had word of a leg injury bothering Beni at the plate in 2019, and it would stand to reason that such an issue could also negatively impact defensive range. I'm not aware of any such explanation for JBJ's defensive nose dive. My personal pet narrative is that the young stud defenders in the OF were dead-legged to a degree (or gimpy-legged in Beni's case) after dominating pole-to-pole in 2018, with only Betts able to hold himself to a more moderate reduction in defensive effectiveness that could just as easily be explained as age-related in terms of speed/range decline.
Getting back to Martin Perez, I see reasons for optimism for this scrap heap pickup, but those reasons are dependent on a number of conditionals.
1) IF Perez is healthy enough to start 29+ games (as he was in 2016, 2017, and 2019)
2) IF Perez really is a FB pitcher now
3) IF Perez's 2nd half slump was influenced at least moderately by the OF defense behind him without Buxton
4) IF Benintendi and JBJ bounce back defensively after freakishly bad 2019 performances
THEN I can see why Bloom may have targeted Perez as a potentially underappreciated asset at a reasonable price. I think my hesitation to buy in on the conditionals above comes down to two health considerations - Perez's health, and the health of JBJ and Beni. Setting those aside, though, I have managed to convinced myself that conditionals 2-4 are either true (Perez is a FB pitcher now) or likely (Buxton injury's impact on Perez and JBJ/Beni bounceback), therefore Perez is more than just a dumpster dive signing in terms of potential performance for the 2020 Red Sox.