James Shields is the only pitcher in baseball to make 33 or more starts every season since 2008. (Joe Nicholson/USA TODAY Sports)

This season, behind a who’s who cast of all-star level starting pitching, the Chicago White Sox are three games back in the American League Central and one game above .500, higher in the standings than where the outfit was projected to be. Spearheaded by Cy Young candidate Chris Sale, Chicago’s starting rotation ranks eighth in Wins Above Replacement and eighth in ERA. By all accounts, the Sale-Jose Quintana-Carlos Rodon-Miguel Gonzalez-Mat Latos-John Danks sextet has overwhelmingly exceeded all expectations this year. That strong rotation was bolstered this past weekend when the White Sox acquired James Shields, a 34-year-old right-hander from the San Diego Padres, in a trade.

Shields is the only pitcher in baseball to make 33 or more starts every season since 2008 and accumulate a nine-year string of 200-inning seasons. But he does little to quell Chicago’s glaring weakness: its bullpen.

In the opening month of the regular season, the White Sox’ bullpen was the gold standard, producing the lowest ERA (1.69), second lowest FIP (2.79) and sixth-highest groundball rate (49.4 percent) in baseball. Chicago’s relievers allowed a league-low 13 earned runs in 69.1 innings pitched. Then they accounted for seven losses in May, tied for the second most of any team over that stretch.

Using Win Probability Added, as Fangraphs’ Jeff Sullivan notes, Chicago’s bullpen was nearly two wins better than average through the end of April and nearly four wins worse than average in May. It’s the largest WPA regression among all starting rotations, lineups and bullpens this season.

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If May’s slate of games is in any way predictive of what’s to come for the White Sox, Manager Robin Ventura can look forward to a nail-biting, anxiety-inducing season. Chicago’s relievers ranked sixth in May in gmLI, or a pitcher’s average leverage index when entering the game. Leverage equates to how critical or pivotal a given situation is, so that Chicago’s bullpen gmLI was high speaks to how closely contested the games the White Sox played in May were — which, again, exemplifies why having an offense with some pop is critical, should a team desire late-game scoring.

Looking forward, there are substantive reservations regarding what Ventura can expect from Matt Albers (9.00 May ERA), Nate Jones (7.27 May ERA), Scott Carroll (11.6 May ERA) and David Robertson (6.30 May ERA), who all struggled mightily in May. Should they produce another below-average month of production, the White Sox could find themselves in the bottom five of the league in relief WAR, an area of the standings that has produced nine playoff teams or 12.5 percent of the playoff pool over the past decade. Nearly all those teams touted an above-average-to-elite offense; something Chicago most certainly doesn’t have.

Chicago isn’t out of the playoff hunt by any stretch, but an imploding bullpen could cripple the team’s chances moving forward. Adding Shields is a nice piece, but one that ultimately fails to address the elephant in the room. In a city frightened by billy goats, the White Sox have a more pragmatic reason to assume a postseason appearance isn’t on the horizon: a shaky bullpen facing a downward spiral.