The Washington Nationals offense has been mired in a month long slump. Every day, the Nats make opposing pitchers look like a combo Bob Gibson, Greg Maddux, and Cy Young. How bad is the offense? Are they significantly underperforming, or have they run into a string of pitchers on top of their games?
Let's look at the last 25 days to find out.
Computing the Data:
I went through the box scores of the Nats' last 25 games. I pulled the opposing team's actual ERA for each game. Next, I computed each opposing pitcher's ERA at the start of the game. From that data. I prorated each pitcher's contribution to that game, to come up with the expected opposing ERA for each game.
For example, if the Nats faced a team where the starter pitched 6 innings, a reliever pitched 2 innings, and a closer pitched 1 inning, I computed the expected ERA to be 6/9*Starter ERA + 2/9 Reliever ERA + 1/9 Closer ERA. This allowed me to use the expected ERA for that game played on that day, as opposed to a "team average" ERA, or an ERA computed 3 weeks after the game was played.
Actual vs Expected
With that in mind, here's the actual vs expected opposing team's ERA over the last 25 games, on a game by game basis. ERA is on the left, Nats opponents on the bottom:
As you can see, the Nats have only scored more earned runs than expected 7 times in the last 25 games. (The 14 runs game against Houston was the game where Roy Oswalt was tossed after 2.1 innings.).
Delta from Expected ERA
Here is the delta from the expected ERA:
It's pretty clear that the Nats offense hasn't run into a string of Aces. The expected ERA of the teams faced ranged from a low of 2.139 to a high of 6.140. The fact is (dropping the highest and lowest deltas), the Nats have scored on average .953 fewer earned runs than expected in the last 25 games.
The reasons are many: Nyjer Morgan leads the team in Plate Appearances, but has struggled to get on base. He has also struggled to stay on base, leading MLB in Caught Stealing. At this point, he is an out 7 times out of every 10 plate appearances, and he gets a lot of plate appearances. Cristian Guzman has seen his batting average drop .025 points during this time frame.
Where's the cavalry?
Unfortunately, the Nats only have one solid bat on the bench. Mike Morse has had an excellent season (.390/.457/.634). For whatever reason, Jim Riggleman elects to sit Morse in favor of Nyjer Morgan (.247/.309/.323) and Willie Harris (.152/.242/.324). In fact, Riggleman has given Willie Harris 12 Pinch Hit appearances during this slump to Morse's 5.
Looking at the minor's, there doesn't appear to be anyone knocking on the door. The Nats still have holes in their minor leagues - there won't be any calvalry this year.
Mike Rizzo's philosophy is that the majors are where you produce, the minors are where you work things out. Right now, guys aren't producing. It's time to try something different.