Two-thirds of the way through baseball’s long season, across both leagues, all nine teams in the Western Divisions are still in the hunt for a division title — and also the wild card slot in the National League. Through Wednesday’s games, the best record of any western division team is 57–51 (Oakland), and the worst is San Francisco (52–56). It’s the sort of spread that would make the late NFL commissioner, Pete Rozelle, as passionate a parity partisan as ever there was, a new fan of the national pastime.

Are these nine teams that close in terms of talent and performance? If you look at their runs scored and allowed, and use Clay Davenport’s calculations to adjust for strength of schedule, the spread between the best and worst in the Wests only changes slightly, with the best team winning 60 games (the particularly unlucky Rangers), and the worst still only winning 52 (those same Giants). That’s an eightgame spread instead of five, but generally speaking, most of the teams have performed very close to their predicted performance after adjusting for the strength of their opponents. Only the A’s and Diamondbacks have been notably lucky in outperforming their projections, while the Rangers and Angels have been the least lucky.

Will that difference hold down the stretch, with only a third of the season left to play? Generally, no, because teams tend to revert back toward .500 — what statheads refer to as “regressing to the mean.” A lot of what we’ve covered here is based on what has already happened in the season, but because these teams are so close to one another, deadline deals loom larger than elsewhere in determining the outcome. In the AL West, the Rangers and Mariners made the biggest bids at self-improvement at the trade deadline, while the Dodgers were very active as well in trying to shore up an infield decimated by injuries. Neophyte Rangers GM Jon Daniels made the biggest splash by adding slugger Carlos Lee from the Brewers, and the Rangers also upgraded in their rotation by getting Adam Eaton back from a finger injury.With the additions of Eaton from the DL and Kip Wells from the Pirates, the Rangers are no longer a team that has to rely on the likes of John Rheinecker or John Wasdin to give their offense winnable ballgames, while adding Lee makes for a huge boost to help the Rangers continue to club the opposition.

With everybody this bunched up, particular strengths and weaknesses of the nine teams can play a particularly important part in determining the outcome. Managerial habits, consistent success with certain tactics, and even the “little things” can all end up determining the outcomes for these nine far more than they would in the Centrals or Easts, or for the AL wild card team. What some of the strengths and weaknesses of these nine, and how much can they make a difference?

Athletics: Their pen’s performance is third-best in baseball, behind only the Mets and Twins, but a rotation without Rich Harden is only going to make them slip in the rankings as the season wears on, and their offensive output has been a problem all year, ranking last in the American League, and better only than the Pirates, Cubs, and Rockies.

Angels: Their rotation should improve on its first half performance, now that rookie sensation Jered Weaver has replaced his brother Jeff, and with young lefty Joe Saunders in the wings, they won’t miss Bartolo Colon for any length of time.

Mariners: Manager Mike Hargrove leans pretty heavily on a mediocre rotation, as Mariners starting pitchers have averaged 101 pitches a start, the second-highest total in baseball, but they’ve been protected well by an underrated pen. Will the newly-acquired DH platoon of Ben Broussard and Eduardo Perez give the offense the boost it needs? Probably not, they will likely be an improvement on Carl Everett.

Rangers: The Rangers have the worst starting pitching of any of the nine teams, ranking 26th in baseball in Fair Runs Allowed, a metric that counts the number of runs a pitcher can expect to give up, including the baserunners that he hands off to the pen. Getting Eaton and Wells should make a huge difference, but there’s still the pen to worry about, which ranks fourth in blown saves.

D-Backs: The Snakes’ middle infield ranks third in baseball in converting double-play opportunities. Led by noted groundballer and staff ace Brandon Webb, their pitching staff generates more groundballs than any team in the game.

Dodgers: Losing Jeff Kent and Nomar Garciaparra to injury puts more pressure on rookie Andre Ethier and big-money star J.D. Drew to get it done, while Greg Maddux will not significantly upgrade a rotation that’s gotten more than expected from Aaron Sele, and what it deserved in thinking former Tampa Bay punching bag Mark Hendrickson had turned a corner.

Giants: It doesn’t get brought up much, but the Giants’ pen has been awful this year, ranking 28th in terms of what they’ve done collectively to secure a win, or lineup-adjusted Win Expectation above Replacement (WXRL). Newly-acquired relievers Mike Stanton and Vinnie Chulk won’t significantly improve that, handicapping the Giants’ shot the postseason.

Padres: San Diego has the best defense in the league when it comes to turning balls in play into outs, and perhaps the best one-two punch in the pen in closer Trevor Hoffman and setup man Scott Linebrink. The Padres are also an underrated offensive ballclub, ranking among the best base-stealing teams with an 80.4% success rate and 86 steals.

Rockies: Owners of the most underrated rotation in baseball, the Rockies rank first in the National League in Support-Neutral Value adjusted for opposing lineups (SNLVA). Whatever else is lowering run-scoring in Coors from historic highs to normalcy, you can’t discount the effect of having the young trio of Jeff Francis, Jason Jennings, and Aaron Cook all simultaneously blossoming as big league horses in the rotation.

Ms. Kahrl is a writer for Baseball Prospectus. For more state-of-the-art analysis, visit baseballprospectus.com