The most important ingredient in defense is pitching, but you also must catch the ball and throw the ball. Boston has a tight defense compared to Houston. If you go to metrics Boston has a 27.8 UZR and 3.8 UZR/150. Houston is -26.3 UZR and -3.4 UZR/150. The Red Sox had 44 Defensive Runs Saved for second in the league and the Astros had -19 DRS. Then there are the matchups by position and I will start with catching.
Boston has speed on the bases. Not one exceptional base stealer like Jacoby Ellsbury, but a collection that can take an extra base and steal a base. Boston’s catchers caught 39 in 99 attempts for 39%. Houston was awful with only 14 captured in 116 attempts. This was a figure I found to give a bit of promise for their notoriously aggressive Boston base runners. Advanced metrics have Boston ranked first in catching and Houston 14th.
The Astros are ranked last at first base in defense and Boston is fourth. At short and second Boston enjoys a smaller advantage, but still an advantage. Either as a group or with the major performers at those positions. Where Houston has a slight edge is with Rafael Devers and Houston’s Alex Bregman. Bregman is ahead of Devers, but both are negative in UZR/150.
The outfield for Boston is exceptional. Mookie Betts and Jackie Bradley are about as good as it gets. In left field, both teams are metric close with Houston slightly ahead on metrics scorecard. What Boston does have is balanced defense with Devers being the only real defensive issue and Boston will undoubtedly substitute late in games for Devers if they have a lead.