David Aardsma played just one season for the Red Sox (2008) and was only marginally effective. But over his eight-year career, he's proven to be a valuable arm out of many other bullpens (i.e., Mariners, Mets, Yankees, Cubs, White Sox, Giants). In what we consider to be the key measure of reliever value (hits per innings pitched), Aardsma has a solid career differential (+35.1). In March, the Cardinals signed him as a minor league free agent. But, on May 15th, if he doesn't get a Red Bird roster spot, he can opt-out of the deal and sign with anyone. In AAA, he's posted a 1.98 ERA with 12 Ks over 13 2/3 innings. Could Ben Cherington be monitoring his decision from afar—in need of some stability in the Boston 'pen? Stay tuned.