In previewing the rosters and defensive alignments for this series, both teams will feature plenty of question marks as to who will premier in the bullpen, but the starting line up is rather set in stone.
AVG/OBP/SLG -- unless otherwise noted
CF Jacoby Ellsbury (L - .298/.355/.426)
RF Shane Victorino (R - .294/.351/.451)
2B Dustin Pedroia (R - .301/.372/.415)
DH David Ortiz (L - .309/.395/.564)
1B Mike Napoli (R - .259/.360/.482)
LF Jonny Gomes (R - .236/.347/.447 vLHP)
C Jarrod Saltalamacchia (S - .273/.338/.466)
SS Stephen Drew (L - .253/.333/.443)
3B Will Middlebrooks (R - ..273/.328/.455 vLHP)
The Red Sox have owned the highest offensive WAR (36.6) and wRC+ (115) for much of the season, and much of that has come from consistent performance high in the line up. The oft injured Jacoby Ellsbury recently fractured a navicular bone in his right foot and was listed as Day-to-Day on Sept 6.
It's possible that Ellsbury will be benched against left-handed pitching (wRC+: 78 vLHP, 133 vRHP), moving Victorino to center (an even trade in defense) and Daniel Nava to right field. When the Sox face right handed pitching in Tampa, Gomes will presumably sit for Nava (another even trade in defense).
Middlebrooks was a pox upon his house in the first half of the season (.267 wOBA, 60 wRC+), but was sent to the minors and tweaked his swing. Since August, he's improved to .344 wOBA and 114 wRC+, though much of that is along his better platoon split. The improvement came just in time for Boston to trade away Iglesias for the likes of Jake Peavy.
C David Ross (R - .216/.298/.382)
INF Xander Bogaerts (R - .250/.320/.364)
OF Daniel Nava (S - .303/.385/.445)
DH Mike Carp (L - .296/.362/.523)
OF Quintin Berry (L - defensive replacement)
Two of these bench players should not be trusted to play defense. I'll let you guess which ones.
David Ross is among the top catchers in framing metrics, and may have earned more playing time if not for a nasty concussion suffered in June. The former Tigers outfielder Berry was a late season acquisition, and he has eight at bats since joining the Red Sox in roster expansions. Xander Bogaerts is a hype machine, and will probably be very good, but right now the veteran Stephen Drew is holding down the fort at short.
I would be remiss to mention that every pinch hitter has been absurdly good for the Red Sox this season. As Zachary Levine pointed out, Boston has the highest OPS for pinch hitters (.923), while the Rays are tenth (.594); conversely, the Rays have pinch hit more than any other team this season (189), while Boston was ninth (92).
One other thing of note: Expect the Red Sox to steal a lot of bases. They nabbed 123 bags this season, third most in the American League. Ellsbury leads the team with 52 swiped, Victorino second at 21, and Pedroia has 17. No one else has more than six.