The Boston Red Sox have the worst starting rotation ERA (5.71) in the MLB, but have still managed to win nine of their first 15 games. When will this become enough of a concern for general manager Ben Cherington to make a trade?

It's still a young 2015 season, but it's clear the cast of Clay Buchholz, Rick Porcello, Wade Miley, Justin Masterson and Joe Kelly needs work. Buchholz, who was once suspected to take over as the staff's No. 1, has a 6.06 ERA; Porcello just signed a four-year, $82.5 million extension, but is 1-2 with a 6.63 ERA in his first three starts; Miley signed a three-year extension worth $19.25 million and has a 6.08 ERA; Masterson is undefeated (2-0), but has surrendered 10 earned runs in 15 2/3 innings (5.74 ERA); and Kelly is perhaps the lone bright spot with a 4.08 ERA in three starts.

Calls for Cherington to trade for Philadelphia Phillies starter Cole Hamels are perhaps echoing throughout Fenway Park, but manager John Farrell isn't too concerned yet about the struggling rotation.

"We're still about winning every night as best we can. I'm hopeful, and certainly expect, that our starters will get to that 21-outs plateau rather than 15-plus," he told Nick Cafardo of the Boston Globe.

After all, the staff is fairly young. Porcello has a lot of experience, but he's still only 26 years old, and so is Kelly, who has made only 51 starts in his four-year career. Miley, 28, is in his fifth season, but he has only three seasons under his belt as a full-time starter. Each of these starters is also dealing with a change of scenery after coming over from the Detroit Tigers (Porcello), St. Louis Cardinals (Kelly) and Arizona Diamondbacks (Miley).

We're also not even three full weeks into the season, so it's clear the staff is trying to get into a rhythm.

"There is precedent for this group of Sox starters to get into the seventh inning, which is what team officials thought would happen. If it's a case of pitchers trying to build up to it, then April is the time," writes Cafardo.

"Farrell doesn't think pitchers get to their optimum strength until mid-May. The numbers have not been good so far, but the situation is improving."

Boston has been in talks with the Phillies since last July regarding a trade for Hamels, but the two sides have been unable to work out a deal because rumors have suggested Philadelphia's demands are excessive. Perhaps that's their strategy as they could be banking on another club to be desperate for an established starter by the time the trade deadline approaches so they can get what they want.

The Red Sox have made up for their inept starting rotation with the sixth-best offense in the MLB, which has scored 76 runs in the team's first 15 games. However, the club is batting just .238 (19th in the MLB) and a more offensive balance will be required if they have to keep picking up the slack for the rotation.

Right now there's no panicking because the Red Sox are atop the AL East with a 9-6 record, but they have three series coming up against the Baltimore Orioles, Toronto Blue Jays and New York Yankees, which could change Cherington's thought process if his starters keep getting shelled by division opponents.