Red Sox fire pitching coach Juan Nieves

Amid relentless struggles on the mound this season, the Boston Red Sox relieved pitching coach Juan Nieves of his duties Thursday afternoon.

Despite bolstering their rotation with a number of prominent starters this winter, the Red Sox have allowed more runs per game than every other team in the American League through the first few weeks of the season.

Nieves, who took over as pitching coach prior to the 2013 campaign, oversaw a staff that owns the fifth-worst park-adjusted earned run average in baseball and a rotation that has posted a smaller percentage of quality starts than all but eight clubs.

"Nothing happened specifically recently that precipitated this," general manager Ben Cherington told WEEI's Rob Bradford.

Though the club's starters have uniformly struggled, however, some regression should reduce the gap between their ERAs and their comparatively stronger peripheral statistics. The staff's relatively high .305 batting average on balls in play, meanwhile, belies its 27 percent hard-hit ball rate, the sixth-best mark in the AL.

Nieves, 50, previously served as bullpen coach for the Chicago White Sox following a brief but memorable stint as a starter for the Milwaukee Brewers. During his truncated playing career, Nieves became the only player in Brewers history to record a no-hitter and remains the only player from Puerto Rico to accomplish the feat.

Cherington is considering one external and one internal candidate to replace Nieves.

Cleveland Indians Triple-A pitching coach Carl Willis is believed to the external candidate being discussed, according to FOX Sports' Ken Rosenthal.