Cardinals news from a Sabermetric point of view

What’s wrong with Mujica?

Cardinal closer Edward Mujica surrendered a home run to Todd Helton and blew the team’s one-run lead in the ninth inning Thursday. It was his second blown save in his last six appearances and the fourth game in his last seven in which opponents reached him for at least one run. After a streak of 18 scoreless outings during July and August, has Mujica lost his touch now that the calendar has flipped to September?

To find out, let’s look at Mujica’s season not with the myopic focus of individual game performances but with the widened peripheral vision of seven-game periods, which afford us a better look at the life of a reliever, who in pitching stints of one to two innings at a time by definition performs in small samples. We’ll use seven-game moving averages of Mujica’s ERA as well as expected FIP (xFIP):

mujica-suddenly-worse

Mujica’s ERA certainly has ballooned since Aug. 21, which, since we’re using seven-game intervals, doesn’t show up until a week later on the chart.

But check out his xFIP during that scoreless run that started on Jul. 5 (reflected in the chart around Jul. 14): It has increased, yes, but not nearly as much as Mujica’s ERA. The more important point is that his xFIP reveals that he was never as dominant as his ERA suggested, undoubtedly contributing to a false sense of security with Mujica as closer.

This of course isn’t to say Mujica is a failure. After all, his season FIP and xFIP numbers are still respectable, if perhaps not what one hopes for in a high-leverage man. A second point is that just because Mujica is giving up runs lately he can’t or won’t “bounce back” — from an earned runs perspective, anyway — since after all he reeled off his earlier scoreless streak on the heels of an even worse period at the end of June. We put that in scare quotes, of course, since when we consider xFIP, Mujica really doesn’t have much to bounce back from.

So yes, Mujica has been a bit worse lately, but only compared to the short period of work in mid-July and even then not as bad as his ERA suggests. He’s basically the same pitcher that the team has had all season. Surely Mike Matheny and the staff are smart enough to have known that the lights-out Mujica they saw back in July and August didn’t mean that they had stumbled onto a late-blooming Mariano Rivera and that their closer was due to regress — especially had they been monitoring his xFIP, which revealed what they had all along.

One Response to “What’s wrong with Mujica?”

  1. Brandon Says:

    Most interesting thing about Mujica is that he really has been pretty much the same guy. He doesn’t walk anybody, he doesn’t strike many out. He’s going to be vulnerable to runs of hits because of that, particularly given the Cards’ subpar defense (which tends to be a bit better due to substitutions when Chief comes on).

    Only real trend I am seeing is in an ultra small sample size, which is a declining K rate. Hasn’t been striking many people out in August and September even by his usual standard. OTOH, is that a reliable indicator when adding five more strikeouts largely makes it disappear? Evaluating bullpens is hard.

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