How other pitchers "Control" The A's

So I've been wondering why Pitchers like Ervin Santana dominate us, and at the same time, we hit decently against better pitchers such as AJ Burnett. My theory, which may not be surprising to many of you, is that pitchers with good control (who do not issue walks) absolutely destroy the A's. Even though this may be obvious, I want to take a closer statistical look at the issue.

Scope: I used statistics from 95 starts against the A's in 2008. These 95 starts came from only 76 starters. This is because some starters have played the A's multiple times (for example, Garland has started 4 times vs. the A's this year).

The relationship between opposing starters' walk rate and the number of runs the A's score:

On the Vertical Axis, I've placed the ERA posted by the opposing starter in their start vs. the A's. On the horizontal axis is that same starter's Walks per 9 innings in 2008. So, for example, the point at (2.5,20) represents a start by James Shields, who posted a 20.32 ERA in his start against the A's, despite having a 2.33 BB/9.

Next, I ran a linear regression on this data, and found that OPPERA = 1.3*BB/9 + 1. In other words, this model predicts that a pitcher who has a 2.0 BB/9 would post a 3.6 ERA in his start against the A's. For each additional BB per 9, a given pitcher will allow an additional 1.3 runs. Note that this is only a model (and the r-squared value for the regression was only .2811). So BB/9 has substantial predictive value for how a pitcher will fare against the A's, but isn't perfect.

So now, I'm sure you're thinking that this was a lot of work for nothing. After all, it's obvious that pitchers who issue a lot of walks will issue a lot of runs. Well, here's where it gets interesting.

The Relationship between a starter's 2008 ERA and his 2008 BB/9

So I was curious whether Walk Rates predict overall ERA's vs all MLB teams in the same way they do vs. the A's. In other words, is the model in the section above similar to the relationship we see for starters in general.

The Plot above uses the same 76 starters (IE the ones who played the A's) and investigates the relationship between their walk rate and their ERA.

Here, the correlation is stronger (R squared = .4), but the slope is much less pronounced. For a typical starter, an increase of 1 walk per 9 innings resulted in only a .39 increase in their ERA.

So, against all of MLB, for these starters, giving up one more walk cost them only 0.4 of a run, but against the A's, it cost them 1.3 Runs.

I think this says a lot about the how extremely Patient the A's are, but also how dependent they are on Walks. Another way of looking at this is that if a pitcher has a BB/9 of 1.0 against the A's (IE they focus very very hard on not walking players), the A's would only score 2.3 Runs.(Remember, it's only a model- so don't take this as gospel).

The ultimate point is this- it's good that each additional walk increases the A's scoring substantially, but the steepness of the slope shows that if a pitcher controls his walks, the A's are in deep trouble. They live and die by walks.

Remember, this was based on only 95 starts, and only 75 pitchers. The correllations were statistically significant, but not extremely strong. So, this isn't proof, per se, that the A's live and die by the walk, but it does help support our suspicion that more than other teams, the A's need walks to succeed.