Runzler agreed to a minor-league deal with Boston on Friday, Chris Cotillo of MassLive.com reports.
Runzler appeared in eight games out of the bullpen for the Pirates in 2017, allowing two runs on seven hits while fanning four over four innings. While he's spent the majority of his time in the minors of late, his major-league experience is certainly a perk for the Red Sox. Runzler will likely serve as organizational depth at Triple-A Pawtucket to start the 2019 campaign.