Run prevention has fueled the Pirates' turnaround the last two seasons. Between 2011 and 2012, Bucs pitchers posted the third highest ERA in the National League; since 2013, they have the fourth lowest. The intriguing thing about their recent success is that it's been supported by some unimpressive peripheral numbers. Here's the breakdown by NL ranking:
Compared to the top six National League pitching staffs, the Pirates look slightly out of place.
Indeed, the team with which the Pirates share the most similar walk, strikeout and home run numbers is the Phillies. But Philadelphia's ERA is third highest in the NL and 0.69 higher than that of the Pirates.
So, what explains the Pirates' low ERA?
This table has most of the answer:
The most important reason for the Pirates' run prevention success is the implementation and execution of an organization-wide pitching and defensive philosophy, which can be summarized as follows: induce batters to hit a lot of ground balls into an infield of precisely positioned fielders. (More about Pirates' defensive positioning here.)
Execution of the Plan
Over the past two seasons, Pirates pitchers have the highest ground ball to fly ball ratio in baseball, and it isn't very close.
Since 2002 (first year of batted ball data), the 2013 and 2014 Pirates rank first and third, respectively, in GB/FB ratio:
Once a ground ball is induced, aggressive use of defensive shifting has undoubtedly contributed to the Pirates limiting their opponents to the fourth lowest BABIP on ground balls the past two years. (Worth noting: the Bucs have not had a single exceptionally rangy or obviously Gold-Glove-caliber infielder the past two seasons.)
Lots of ground outs means that opposition batters have had fewer opportunities to hit fly balls and line drives. A record low 32.4 percent of all plate appearances resulted in balls hit in the air against the 2013 Pirates, with the 2014 Pirates ranking second with 33.7 percent (since 2002).
(FB+LD/TBF = fly balls plus line drives divided by total batters faced)
The term "air ball" is one you've surely heard only to describe basketball, but it's a useful term for baseball as well. The 2013 Pirates allowed the fewest air balls since 2002, with the 2014 Pirates ranked third.
Fewer fly balls means opposing hitters have had fewer opportunities to hit home runs and extra-base hits. Indeed, the Pirates have allowed the fewest home runs in the majors despite having a HR/FB ratio that is 0.8 to 1.4 percent higher than the four teams behind them.
By limiting the total number of fly balls, the Bucs haven’t had to rely on an exceedingly low and perhaps unsustainable (and certainly volatile) HR/FB rate.
Finally, despite allowing the second highest BABIP on balls hit in the air (AB in the chart below), the Pirates have posted the lowest opposition slugging percentage in the National League the past two years.
As we saw with home runs, by limiting air balls, the Bucs have been able to absorb a higher BABIP rate and still maintain the best slugging percentage against.
The Pirates have induced a lot of ground balls and efficiently turned them into outs, which has directly contributed to the fewest home runs allowed and lowest slugging percentage over the past two seasons.
So, what has the successful execution of their Pirates' run prevention formula meant in terms of runs and wins? In order to find the answer, we turn to a measure of team defense that I developed two years ago called Total Defense Tool (TDT).
I have explained TDT in the past, so some of what follows is lifted from a previous posts on this site.
Total Defense Tool (TDT)
TDT is a runs estimator that uses a modified wOBA formula. The TDT formula is as follows:
TDT: = (LW * # HR allowed) + (LW * #HBP) + (LW * #ROE) + (LW* #NIBB) + (wOBA for ground balls * number of GBs) + (wOBA for air balls * number of air balls)/ Adjusted plate appearances. The TDT coefficient is then turned into total runs created.
"LW" in the equation refers to linear weight of each event. They are updated by Fangraphs.com yearly. (Notice that a separate wOBA coefficient is derived for each batted ball type.)
When we plug the actual National League team totals for the 2013 and 2014 season into the TDT formula, it churns out very accurate results. The TDT estimates a total of 19801 runs allowed by National League teams for the past two seasons. The actual number of runs allowed is 19528 (a difference of 273 runs for 15 teams). The team-by-team correlations between predicted and actual runs scored is .97 and the R-squared is .93.
While TDT is not necessarily the most sophisticated run estimator (though it matches up very well with others), its greatest strength is its flexibility. By simply changing the combination of variables that are set to league average, the impact of different skill sets can be isolated and compared.
For example, one of the things we are interested in is the impact of the Pirates' high ground ball rate. In order to isolate its impact on total runs allowed we simply:
- Plug in all of the Pirates' actual numbers and derive a run estimate.
- Go into the equation and change the number of ground balls and air balls allowed to league-average rates and come up with a new estimate of runs allowed.
- By comparing the two numbers, we derive an estimate of the number of runs that the Pirates have saved due to their ground ball rate, which then can be translated into wins.
To isolate the impact of the Pirates efficient ground ball defense, we simply change the Pirates' wOBA score for ground balls to league average and look at the impact that makes on total runs allowed.
Measuring the impact of the Pirates run prevention formula
The TDT estimates that the Pirates would have allowed 1219 runs since 2013. They actually allowed 1208.
Scenario #1 - League Average ground ball rate
What if the Pirates had induced a league-average ground ball rate that past two years, but had fielded grounders at the same rate of efficiency? In other words, what if the pitchers had not executed their half of the run prevention formula, but the defense was still good?
When the Pirates' GB% is set to league average, they allow 53 more runs, which costs them almost six games over two seasons.
However, that total does not reflect the additional number of home runs that more fly balls would have cost the Pirates. When we add in the additional home runs, we get the following results:
The Pirates' high ground ball rate saved about 95 runs over the past two years and gained somewhere in the neighborhood of 10 wins.
Scenario #2 – Average Fielding
What if the Pirates had induced the same number of ground balls, but fielded them at a league average rate of efficiency? In other words, what if the pitchers had executed their half of the formula, but the defense was just average?
The Pirates defended grounders at a rate .014 wOBA better than league average. It saved them an estimated 45 runs and almost five wins over the past two years.
Scenrio #3 – No ground ball plan in place. League=average fielding and ground ball rate
What if the Pirates had not implemented or successfully executed their run-prevention plan? In other words, what if their pitchers threw a league-average number of grounders and the defense was just average?
The Pirates saved an estimated 137 runs and gained 15 wins by successfully inducing and then efficiently fielding ground balls.
The Pirates dramatically improved their run prevention the last two seasons and as a result they’ve made it to the postseason twice. However, they have not saved runs by striking out a lot of opposing hitters, or limiting walks, or even getting lucky on fielding line drives or a low FB/HR rate. Rather, they have concentrated on forcing opposing hitters to hit ground balls into creatively positioned defensive alignments. The successful execution of their pitching and defensive philosophy has gained the team an estimated 15 wins over the course of the past two seasons.
(All statistics courtesy of Fangraphs and Baseball Reference)