As I mentioned in our last post, Johan Santana has an acceptable 4.24 ERA over his last 9 starts, but very poor peripherals. During this span, Johan has struck out 4.9 batters per 9 innings and walked 3.0. The walk rate is a little high, but I'm more alarmed by the strikeout rate. Just to make things a little more precise, Johan has struck out 12.8% of the batters he's faced in his last 9 starts; over his career, his rate is 25.2%, almost twice as high.
This seems like a pretty bad stretch, but maybe it's not uncommon. Maybe Johan has had bad stretches like this before and bounced back. I was curious, so I made a spreadsheet of every career start since Johan permanently became a starting pitcher in 2003. Until this season, his worst 9-game stretch in K% was 17.0%, which came during a July-August stretch last season (before that, it was 17.2% during July-August 2005). His lowest K/9 was 6.4. So, a K% of 12.8% and a K/9 of 4.9 is easily the worst 9-game stretch of his career.
As I mentioned, his walk rate has been poor, too. Put the two together, and you have a weak 1.6 K/BB ratio over the last 9 games. Before 2009, Johan's worst 9-game stretch was a 2.4 K/BB during the 2008 lull (he's had a couple other dips to 2.6 during his career). Again, the current stretch is significantly worse than any prior stretch of his career.
Maybe I'm being too selective by focusing on 9 games. So, I looked at his worst 5-game stretches. During this current stretch, his worst 5-game numbers are a 10.7 K% and a 1.1 K/BB. His previous lows were 14.4 K% and 1.9 K/BB (different seasons). His current 5-game lows are a lot lower than any previous ones. Even his current 9-game lows are worse than any prior 5-game stretch.
I don't really have an answer to my original question. I'm not sure how worried we should be, but it's clear from the numbers that Johan's going through the worst stretch of his career.