The regressing Sox rotation: Whose struggles are real and who is due for turnaround?

Aug. 4—Compared to last year's disaster squad, the Red Sox starting rotation has been remarkably durable and adequate through the first two thirds of the season.

None of the regular five starters have missed time on the injured list, and through the first two months the rotation was not only consistent, but legitimately good.

But since the start of June, the group has begun regressing and the entire rotation largely struggled throughout the month of July. Now what once looked like a strength is starting to look more like an anchor on the team's playoff hopes. With no additions at the trade deadline, Boston is counting on improvement, as well as the boost provided by Chris Sale's imminent return.

So whose struggles are greatest cause for concern and who is most likely to turn things around? Here's a look at each Red Sox starter, from most problematic to most likely to earn a spot in the postseason rotation.

Garrett Richards

When Sale is ready to make his big league return, Richards is the most likely candidate to be bumped from the rotation. In 10 starts since June 1 leading into Tuesday night in Detroit, Richards posted a 6.65 ERA while averaging only 4.2 innings per start. Worse, opponents batted .335 against him with a 1.005 OPS and his WHIP was a dreadful 1.83, meaning he'd averaged close to two baserunners allowed per inning.

With numbers like those, it's no surprise that Richards hasn't posted a quality start since June 1 at Houston, a streak that stretched to 10 with his shaky 4-inning outing on Tuesday.

Martin Perez

Dumping on Richards has become trendy among Red Sox fans this season, but the truth is Perez hasn't been any better. In his last 10 starts since pitching 7.2 innings of scoreless baseball June 3 against the Astros, Perez has posted a 6.69 ERA with only one quality start. Hitters are batting .351 against him with a 1.030 OPS, his WHIP is 1.85, and he's failed to even reach the fifth inning six times during that stretch.

The one thing working in Perez's favor is that while he's struggled to pitch deep into games all season, he did go at least five innings with three or fewer runs in nine of his first 11 starts. If the Red Sox can get that version of Perez back, he could still be a useful contributor.

Eduardo Rodriguez

Unlike the others who have been hit or miss, Eduardo Rodriguez has been consistently mediocre all season. His ERA is 5.60, and over the last 10 starts it's sitting at 5.55. That's obviously not good enough, but there's reason to believe improvement is possible.

Since June 1, Rodriguez has pitched into the sixth inning five times with three quality starts, and opposing batters have hit .265 with a .745 OPS, far more respectable numbers than those posted by Richards or Perez. His 1.38 WHIP is also decent. One major red flag, however, is that his batting average on balls in play (BABIP) over that stretch is .367, suggesting that when hitters have made contact, they're hitting the ball hard.

Nick Pivetta

Nick Pivetta has been Boston's second-best starter after Nate Eovaldi, but his recent downward plunge is concerning. Over his last 11 starts, Pivetta has posted an ERA of 5.22, and in each of his last four starts he's either allowed four runs, failed to get out of the fifth inning or both.

The upside is that he's still holding batters to a .251 average and a .801 OPS while posting a WHIP of 1.36 and BABIP of .295 since June 1, all of which are numbers the Red Sox will take from a No. 3 or 4 starter. Pivetta has also been excellent the days where he's on, the most recent example being his seven inning, scoreless, 10-strikeout gem against Oakland July 4.

Tanner Houck

Could Houck slot in as the No. 3 starter behind Sale and Eovaldi in the playoffs? The numbers suggest he deserves a shot. Since coming back off the injured list in July, Houck has posted a 0.77 ERA while holding opponents to a .125 average, .355 OPS and .227 BABIP. His WHIP is a microscopic 0.77 and he's earned rave reviews for his electric stuff.

The two things working against Houck? He's never pitched in a playoff atmosphere and hasn't pitched more than five innings once all year (in the big leagues or in Triple-A). But if you can get four dominant innings out of Houck and hand the ball to Garrett Whitlock in a playoff game, wouldn't that be as good an option as the Red Sox have?

Nathan Eovaldi

His last outing aside, Nathan Eovaldi has been really good this season and the Red Sox are lucky to have him. He's posted a 3.71 ERA on the year to earn his first career all-star nod, and since June 1 has an ERA of 3.41 while pitching into the sixth inning in eight of 10 starts. During that stretch he's held opponents to a .267 average, .727 OPS and has a WHIP of 1.20, and overall his 2.5 Wins Above Replacement (WAR) ranks 15th among American League pitchers.

The one concern is that Boston has lost Eovaldi's last four starts, but even that is a bit misleading given how one of those losses was in the Yankees' wild eighth-inning comeback, where Eovaldi pitched brilliantly. Short-term hiccups aside, Eovaldi gives the Red Sox a chance to win, and he'll be a key factor down the stretch.

Email: mcerullo@northofboston.com. Twitter: @MacCerullo.