The rookie second baseman is 4 for 51 (.078) with 17 strikeouts and one walk in his last 12 games. The slump dropped his OPS from .935 to .708. It has been a struggle defensively, too. Metrics show Campbell to be one of the lowest-rated players at his position in the majors.

Campbell did first-base drills before Friday's game in Boston while Mayer prepared for his sixth start at second for Triple-A Worcester.

Kristian Campbell can play almost any position – and has – but on Friday afternoon he began working somewhere new. As Red Sox teammates and staff, including manager Alex Cora, looked on, the rookie went through first-base drills.