Baseball goes to great lengths to make projecting playoff performance hard. It’s not just that postseason series are too short to definitively determine the better team in any given matchup; it’s also that the season stretches so long that a team’s April roster (and coinciding stats) may have little bearing on its October composition, particularly since the postseason schedule allows teams to deploy its players differently, bypassing fringy fifth starters or even skipping starters entirely. Those analytical hurdles distort our understanding of each team’s October true talent, making it tougher to tell who has the upper hand. Judging by their regular-season record, the Red Sox were the best team in baseball by five games. And judging by the AL East standings, the Sox were significantly better than the Yankees, whom they beat by eight games. (Only the Indians, in a historically awful AL Central, won their division by a wider margin.) Based on that surface performance, then, Boston should be favored to win the first Sox-Yanks playoff rematch since the back-to-back ALCS showdowns in 2003-04, which begins at Fenway on Friday.

Dig a little deeper, though, and the teams in the Red Sox’s rearview mirror are much closer than they appear—or, perhaps, appear to have passed them. By measures such as BaseRuns and third-order record, which strip away the sequence in which teams distributed their runs, the Astros were the best team in baseball and the Yankees were barely behind Boston: BaseRuns puts the Boston-New York gap at 10 points of winning percentage, while third-order record says the separation was a single point. The Red Sox only slightly edged out the Yankees in their season series, 10-9, which probably reflects the teams’ true proximity. Even then, though, we’re looking at full-season stats, including performances by players who aren’t on current rosters. Focus solely on the players eligible to appear in the division series, and any edge that Boston appears to possess evaporates: According to FanGraphs, the current Red Sox roster ranks fourth in the playoff field in projected winning percentage, with the Yankees taking the top spot. No wonder New York is so confident.

Most of that difference is attributable to the bullpen. The current Red Sox pen would project to be worth 4.9 WAR through a full season, better than the Rockies’ and Braves’ relief corps but worse than the other surviving playoff teams. The Yankees’ pen laps the field with a projected 9.5 WAR, nearly double Boston’s total. Granted, the projections treat Boston’s bullpen-bound starters (Eduardo Rodríguez, Steven Wright, and possibly Nathan Eovaldi, who’s scheduled to start ALDS Game 4) the same in the pen as they would in the rotation, which may underrate their relief ability. But however one slices the stats, it’s almost inarguable that Boston’s bullpen, which lost Carson Smith and Tyler Thornburg to season-ending injuries and which president of baseball operations Dave Dombrowski didn’t bolster by trade, is considerably weaker than New York’s super-pen, which absorbed Zach Britton into a group that already included Aroldis Chapman, a resurgent Dellin Betances, Chad Green, and David Robertson, among other arms. Craig Kimbrel, Matt Barnes, and Ryan Brasier give Boston a few appealing late-inning options, but Sox skipper Alex Cora can’t match the parade of dominant right- and left-handed arms that Aaron Boone can deploy from the middle innings on, as he did for the final five innings of the Yankees’ win in the wild-card game on Wednesday.

In a year when relievers for the first time accounted for more than 40 percent of regular-season innings and may surpass 50 percent in the postseason, the Red Sox aren’t equipped to win a war of relievers with the AL’s best bullpens. “We work differently than other teams,” Cora told reporters on Thursday afternoon. “We relied on our starters throughout the season. They carry us.” That model makes it imperative that they continue to get quality and length from their rotation, which in turn trains the spotlight on Sox starter Chris Sale, whose uncertain status is of central importance to the team’s hopes this month.

On an inning-per-inning basis, Sale was at worst the second-best starter in baseball this season, behind Jacob deGrom; factor in his home park and the quality of the competition he faced, and he has a strong claim to edge out the Mets ace. Like the league as a whole, Sale has reduced his sinker usage as the season has progressed. In March and April, he threw the pitch almost a fifth of the time, but he’s all but eliminated it in August and September. That may have made him even better, given that the sinker has been his worst pitch both in the past and in 2018, and also considering that Sale has a top-10 four-seamer and changeup and a top-15 slider among starters with at least 100 innings thrown this season. If Sale doesn’t win the AL Cy Young Award, it will be because he threw only 158 innings and finished four frames short of qualifying for the ERA title. But the fact that he fell short of that (admittedly arbitrary) threshold points to a problem that’s plagued him before.

Long reputed to be a potential injury risk because of his unorthodox delivery, Sale has instead been a model of durability. Since the southpaw became a starter in 2012, only five pitchers have amassed more innings than he has, and only Clayton Kershaw and Max Scherzer can match him WAR for WAR. Prior to this season, he’d hit the DL only twice, for an elbow strain in 2014 and a fractured foot in 2015. Both of those injuries—as well as the case of shoulder tendonitis that rendered him day-to-day in 2013—struck early in the season. Yet Sale has exhibited a clear pattern of tailing off in performance as the season wears on. The table below lists the active pitchers (minimum 500 career innings pitched) with the worst regular-season stats in the second half and in September and October, relative to their own overall lines. The higher the tOPS+, the higher the pitcher’s OPS allowed, compared to his career average.

Late-Season Swooners: Worst Second-Half and Sept./Oct. Splits Among Active Pitchers, Min. 500 Total IP Player G GS IP Second-Half tOPS+ Player G GS IP Sept./Oct. tOPS+ Player G GS IP Second-Half tOPS+ Player G GS IP Sept./Oct. tOPS+ Chris Sale 134 88 627.1 117 Chris Sale 57 36 238 141 Andrew Miller 212 23 278.2 116 Aaron Nola 16 16 94.2 133 Jesse Chavez 205 16 307.2 115 Matt Harvey 19 18 97 132 Johnny Cueto 118 118 709.2 115 Chad Gaudin 63 11 119 131 Jim Johnson 281 2 278.1 115 Jesse Chavez 86 2 94.2 128 Tyler Chatwood 63 49 259 114 Edward Mujica 80 4 90.2 128 Dan Straily 68 61 350.2 114 Jeanmar Gómez 56 13 108 127 Jordan Zimmermann 101 100 568.2 114 Andrew Miller 98 8 113 126 Matt Albers 244 14 316 113 Fernando Rodney 176 0 172 125 Alexi Ogando 117 20 195.2 112 Johnny Cueto 49 49 289 120

No other active pitcher has seen his performance suffer late in the season like Sale, whose stringbean build may not be built for the long haul. That’s not including his brief playoff history: Sale took two losses in last year’s ALDS against Houston and allowed four homers and nine runs in 9 2/3 innings, although he pitched better in his Game 4 relief outing than his final line suggests.

Let’s not make this more than it is: Even at his worst, in September and October, Sale has recorded a 3.84 ERA as a starter, with an identical FIP. That’s what a best month might look like for some passable pitchers. But against the league’s best lineup, which is fully healthy for almost the first time, the Sox need Sale at his best, not his worst, no matter how competent the diminished model is. And during the course of his career as a starter, Sale has been at or close to his worst in almost every area in the last month of the regular season, from his four-seamer speed to his strikeout-minus-walk-rate to his home run rate to his hard-hit rate.

Chris Sale’s Career Monthly Splits As a Starter Month ERA FIP FA Velo K-BB% HR/9 BABIP Hard % Month ERA FIP FA Velo K-BB% HR/9 BABIP Hard % Mar/Apr 2.67 2.84 93.6 21.8 0.7 0.265 25.8 May 2.6 2.56 94 25.8 0.7 0.251 26.3 June 2.6 2.47 94.4 26.3 0.7 0.283 25.3 July 2.47 2.47 94.4 25 0.6 0.317 28.2 August 3.37 2.99 94.1 26.4 1.1 0.307 26.6 Sept/Oct 3.84 3.84 93.3 23.2 1.5 0.336 34.9

Unfortunately for the Sox, there’s even more reason to stress about Sale this season than usual. The lefty was sidelined in the second half of the schedule for a total of almost 40 days by two DL stints for shoulder inflammation, and he made only five starts after the trade deadline and four after August 12. When he was on the mound, the Sox handled him carefully, and he lasted no longer than 4 2/3 innings in any of his September outings; he hasn’t seen the sixth since July 27. Granted, Sale still struck out 18 men in his 12 September innings, versus only one walk, but amid his shoulder woes, his fastball speed sank precipitously. His 90.2 mph average four-seamer in his most recent start on September 26 was a career low, and his 94.7 mph max velocity in that outing was his lowest since the spring of 2014.

On Thursday, Sale didn’t offer any answers about the mysterious speed decline in his last start, saying, “It’s a game, what are you going to do? Sometimes you go out there and you have your best, sometimes you don’t.” Cora has insisted that Sale is healthy—not that he or, for that matter, Sale would necessarily divulge any lingering discomfort right before the playoffs—and pitcher and manager alike have previously pinpointed poor extension stemming from a shortened or misaligned stride as the culprit for his loss of speed. It’s true that Sale’s extension—how far in front of the rubber he releases the ball—has dropped in recent starts, although not quite to seasonal lows.

To the naked eye, Sale actually looked less explosive at the end of the season ...

... than he did in mid-July.

It’s completely possible for a great pitcher to suffer from a fleeting bout of mechanical complications, especially after an injury, when he might unwittingly change some aspect of his delivery in an effort to protect the compromised part. In July, reigning AL Cy Young Award winner Corey Kluber went through his roughest stretch since his rookie season, which was caused by mechanical quirks brought on by a sore right knee, but he began to dominate again as soon as he straightened out the issue. Sale says the time off since his last start has allowed him to work on “using my legs, driving a little bit more” and “getting a little more rotational with my lower half and staying stronger with my top half.” If he’s healthy, the lefty’s light workload thus far could help him stay fresh deep into October. As Cora acknowledged, though, we won’t know whether those attempted tweaks worked until Sale starts working against Aaron Judge, Giancarlo Stanton, and the rest of the Yankees’ prodigiously powerful lineup.

According to Cora, Sale is “a full go” for Friday’s start, with no abnormal constraints on his pitch count. And it sounds as if Cora is prepared to push him, whether or not Sale’s stuff has returned. “If he goes up to 99 or he’s throwing 95 or he’s throwing 91, he’s still a great pitcher,” Cora said. Maybe—but not equally great. Even aces have degrees of dominance, and Sale’s varies more than most.

On Thursday, a reporter asked Sale, “Chris, can you talk about your success against the Yankees this year?” Sale responded with one word: “No.”

Reporter: "Chris, can you talk about your success against the Yankees this year?"



Chris Sale: "No." pic.twitter.com/AjCxnNq2k9 — SportsNet New York (@SNYtv) October 4, 2018

Sale was brilliant in two starts against his ALDS adversaries this season and allowed one run over 13 frames with 19 strikeouts and one walk. But we probably shouldn’t dwell on those outings either; Sale made those starts in April and June, and historically speaking, late-season Sale isn’t the same as early or midseason Sale. It would, of course, be too simplistic to say that any series will swing based on one player’s performance, and it’s impossible to predict how any given game will go: On Tuesday (well, Wednesday morning), the Rockies eliminated the Cubs on a hit by baseball’s worst batter, miscast pinch runners aside. But as much as any other factor, the playoff fate of the team with baseball’s best record hinges on whether we see the classic Sale or the September Sale this month.