After a week hiatus, it is time to update the weekly "Return to Average" series.
The story of last two weeks of Pirates’ baseball is the apparent regression of the pitching. Since August 1st, Pirates’ pitchers have allowed 60 runs (5.0 RA/G) and posted a 5-7 record. A steeper drop off in terms of wins has been prevented by the continued steady performance of the offense, 59 runs (4.92 RS/G) and a 105 wRC+ (interpretation: offensive production has been five percent above league average).
The pitching slide can be largely explained by the Pirates’ National League worst HR/FB in August of 16.5 percent (11.3 percent for the season). Fully 50 percent of the runs they have allowed this month have come via the long ball. That is 13 percent higher than both the MLB and Pirates' seasonal average. Fortunately it appears that a steeper pitching regression has been avoided by a combination of luck and good defense. During this short 12 game stretch the Pirates’ BABIP-against has been the third best in the National League, .261. For the season, their BABIP-against remains third best in the National League, .277.
Much, but certainly not all, of the pitching regression has come from a bullpen that has suddenly become very wobbly. After the jump I will first present the weekly RTA runs scored and runs allowed tables and then we'll take a closer look at some of the numbers behind the bullpen's recent troubles.
The Pirates played seven games this week and allowed 41 runs, an average of 5.86 runs allowed per game. Their RA/G for the season increased from 3.8 to 3.9. Last week they needed to average below 3.9 RA/G to finish at 90 percent of NL average runs allowed. That number has decreased to 3.6. For the Pirates pitching/defense to finish with 90 percent of league average RA/G, they will have to allow 17 percent fewer runs than expected NL average runs for the rest of the year.
Last week was the fifth week in a row that the Pirates allowed more runs per game than the week before
Interpretation: goal is to have the red line remain below the purple line. The lines have the same meaning as those in the first graph, except they are for runs allowed.
The regression in the performance of the Pirates' bullpen over the past two weeks is displayed in tables and graphs below. It is important to note that pitching statistics for relief pitchers are more volatile than those of starting pitchers because of the relatively fewer innings that they pitch. Another effect of smaller sample sizes for relief pitchers is that the aggregate statistics for bullpens are generally more resistant to the forces that tend to regress performances to the mean over the course of a season. However, since the Pirates bullpen performed far above expectations for the first four months of season, some slippage was predictable, but not inevitable.
For the first four months of the season the Pirates' bullpen was stranding runners at an historic rate. There has been rather significant drop off in the stand rate the past two weeks.
ERA, FIP and ERA-FIP
The bullpen's ERA and FIP (Fielding Independent Pitching) has ballooned over the last two weeks. Moreover, the negative gap between ERA and FIP, which had been at historic levels throughout much of the season, has reversed and moved slightly in the opposite direction.
Large negative differences between ERA and FIP are generally interpreted as the product of luck or good defense. To the extent that we expect fortuna to even out over the course of six months, a highly negative number is typically taken as a sign that the conditions for some form of regression, in form of allowing more runs, are ripe.
A few weeks ago I introduced the "meltdown" metric. A meltdown is defined by Fangraphs.com as a reliever costing his team a six percent chance of winning. In my July 21st post I showed that at their current pace the Pirates would have the fourth best ratio between shutdowns (adding six percent to the chance of winning) and meltdowns out of the 1078 bullpens for which we have data. As of three weeks ago, the Pirates had a SD/MD ratio of 2.88, with 92 shutdowns to 32 meltdowns.
In first two weeks of August the ratio between shutdowns and meltdowns has evened out some. Over the past 12 games the shutdown / meltdown ratio is down to 1.4.
The Pirates' problems throwing out would-be base stealers is well-documented. Indeed, I have not been able to find a team in the history of baseball that posted a lower CS% for a full season than the Pirates' current pace (9.7 percent). What baffles me is that opposing managers don't seem to be taking advantage of the Pirates problems in this regard. When you divide total number of attempted steals against the Pirates by total number of stolen base opportunities, the Pirates rank only slightly higher than league average. One would expect this number to be much higher. I have no explanation. Perhaps it is related to Pirates' pitchers holding baserunners exceptionally well. Or, it could be that opposing hitters are dis-proportionality reaching base in situations that a stolen base is not worth the minimal risk of being caught. It might just be that opposing managers are being overly conservative. Whatever it is, the Pirates are seemingly fortunate that opposing teams have not attempted more stolen bases. (data from baseballreference.com)
That is all for this week's "Return to Average." I'll return next Monday to update the numbers for Week 19. Until then, enjoy the pennant race!