Foster Griffin to be traded to Guardians (source)

The Guardians are set to acquire a steady arm to their rotation, having agreed to a trade with the Nationals for left-hander Foster Griffin ahead of Monday’s 6 p.m. ET Trade Deadline, a source told MLB.com’s Mark Feinsand. Neither club has confirmed the deal, which will send four Minor Leaguers back to the Nats: Left-handers Josh Hartle (Guardians’ No. 25 prospect) and Will Dion, as well as…