NASHVILLE — The Boston Red Sox further bolstered their bullpen on Monday, agreeing to a trade with Seattle for Carson Smith and Roenis Elias. In 70 games with the Mariners last season, the right-handed Smith had 13 saves and a 2.31 E.R.A., with 92 strikeouts in 70 innings. He will serve as a setup man to Craig Kimbrel, a closer acquired last month from San Diego in return for prospects, with Elias as a long reliever and insurance for the rotation.
The Red Sox sent starter Wade Miley and reliever Jonathan Aro to Seattle.