There are plenty of post-trade deadline storylines to examine as the Boston Red Sox open their series Friday against the Houston Astros, but we shouldn’t lose sight of the Alex Bregman subplot. Bregman will take the field for the first time in his major league career with the Houston Astros in the other dugout. The former Astros first-round pick played nine seasons in Houston, making two All-Star appearances and winning two World Series rings before signing with Boston in February. The third-base slugger came to Fenway Park last August as a member of the conquering party, hitting a pair of back-breaking home runs as the Astros swept the Red Sox and dealt a huge blow to their playoff hopes.