July 20, 2007

Prospectus Today

Upstairs Downstairs Out West

by Joe Sheehan

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Strange doings in the American League West...

Team      Record   Pct     RS   RA
Seattle   53-39   .576    456  445
Oakland   45-50   .474    402  391

The Mariners and A's have the exact same run differential, +11, and yet are separated by nine-and-a-half games in the standings. The Mariners are a contender-two games out in the AL West, and 1 ½ out in the wild-card chase-while the A's are going to play out the string without much hope of a postseason berth for the first time since 1998.

Statheads look at run differential-as opposed to wins and losses-as a measure of team quality because teams don't have the ability to distribute their runs in a manner that causes them to win more often than those two basic measures suggest they should. In any given season, some teams outperform or underperform their record, but those variations have never been shown to be the result of an ability or inability to score timely runs. Bullpens have been shown to have an effect, with good ones enabling a team to win more close games and thus get an edge on their RS/RA. There's some belief that a manager's choice of tactics and personnel in lost causes can skew the numbers, with some teams more prone to turning big losses into bigger ones, which would affect the RS/RA.

In the specific case of the 2007 Mariners, it appears that their record diverges from their RS/RA for two specific reasons: they have the best bullpen in baseball so far, and they've lost some games by a lot of runs. The Mariners are 16-11 in one-run games, 22-14 in one- and two-run games, and over .500 at every stop until you get to five-run games (4-7). At the other end of the spectrum, though, the Mariners have lost five games by at least nine runs, and are 0-5 in games decided by more than eight runs, a deficit of 58 runs in blowouts. (They are, oddly, 5-0 in games decided by exactly eight runs, which makes up most of the gap.) As the bullpen has driven the close-games record, the rotation-due to an unhappy number of disaster starts from Jeff Weaver, Ryan Feierabend, and Horacio Ramirez-has been responsible for those big losses.

You can see, though, that we're not necessarily talking about "luck" here. The Mariners' record in close games and blowouts is tied to their personnel, or at least its performance to date. Whether they can continue to play .576 ball with a .510 run differential is most likely tied to whether their bullpen, which has been insanely great-fourth in WXRL and Adjusted Runs Prevented, led by two guys who've posted an ERA of 0.97 in 74 1/3 innings-can continue to perform at this level. There's enough disconnect between the peripherals and the ERAs of Brandon Morrow and Eric O'Flaherty to project some slippage over the next ten weeks. One key statistic to watch: the top five relievers in the Mariners' pen have allowed seven homers, total, this season. That number is almost certain to rise.

Why are the A's so far off their mark? That's not as simple. They don't have a major shortfall in close games-14-15 in one-run contests, 24-20 in games decided by two or fewer runs-that would explain the gap. They have won some blowouts-4-0, +49 in games decided by double-digit runs-which accounts for some of the gap, but this isn't the kind of offensive juggernaut that can queer its differential with frequent blowouts. The A's actually have one of the worst offenses in the league. The strength of their rotation, defense and low-offense home park have kept them from being blown out, which may be the one differential-skewing factor in play, although it's a small one.

The quirk for the A's is their record in games decided by three or four runs: 6-21. That's hideous, and it's a direct result of the team's inability to score enough to support their rotation. When they allow four or five runs-around a league-average figure and one that should produce something approaching a .500 record-they're a meager 10-20. Unless the A's pitchers keep the opposition under four runs, the team has little chance to win the game. They just can't score.

Run differential is a key measure of team quality, and a better predictor of future performance than win-loss record. With that said, it is worth taking the time to look more deeply and see what has gone into that run differential, and what the reasons are for any gap. The AL West may seem to hold two teams of basically even quality and disparate luck, but it's clear that the Mariners, despite sharing a +11 differential with the A's, are the better team and will continue to be so. A postseason slot may yet be out of reach, but holding off the A's for second place and their highest finish since 2003 is a certainty.

Joe Sheehan is an author of Baseball Prospectus. 
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