Where did Mets closer Jeurys Familia's improved control come from?

Mets closer Jeurys Familia's walk rate has improved significantly over the last three seasons, from 7.59 per nine in 2013 to 3.72 in 2014 and 2.19 in 2015. The 2013 results were in an extremely small sample and after coming off of elbow surgery, but he walked 4.80 batters per nine innings in 137 minor league innings in 2012, so it's not like he had ever been mistaken for Greg Maddux.

Something seems to have clicked with Familia in recent years, to the point where his 2.19 BB/9 in 2015 is decidedly above league average. What caused this change?

The first and most obvious place to look at is Zone%, which is the percentage of pitches Familia threw that were in the strike zone:

2013: 42.1%

2014: 41.7%

2015: 43.8%

Well, that doesn't really tell us anything. An increase of less than two percentage points in Zone% isn't significant enough to represent a real change in approach. For reference, league average is around 45% every season, so despite Familia's sterling walk rate this year, he was still below average in terms of throwing pitches that are in the strike zone. This would seem to signal that Familia's change in walk rate was due to luck or random happenstance, and that he would be likely to regress this season.

There are other plate discipline stats, however, that say otherwise. Take a look:

Let's focus on the left-most column first. F-Strike% represents the percentage of Familia's first pitches in every at-bat that result in a strike—whether it's called, a swing-and-miss, or the batter makes contact with it. Familia made a major jump in this category in 2015. There are three main reasons why most of Familia's first-pitch strikes are going to be called strikes:

1. He has a lot of movement and velocity on all of his pitches, so hitters are going to be especially willing to take the first pitch to note his release point, along with the movement, deception, and speed of the pitch.
2. The old scouting report on Familia is that he's wild, and taking pitches against a pitcher with poor command is often a good idea.
3. Familia pitches most of his innings late in the game. Many of them come in the ninth inning, where many hitters are told to take until they get a strike.

This means that the data may indicate an actual skill change in Familia's control. A conscious effort to throw more first-pitch strikes means that he's able to throw his pitches with greater command. It is important to note that recent research has shown that the first-pitch strike isn't as important as many baseball adages make it seem. However, the data shows that getting to a 1-2 count rather than a 2-1 or 3-0 count is the most pivotal part of the at-bat, so a first-pitch strike is still technically incredibly important because it's a means by which to get to that desired count. It also sets up the other columns in the table.

Swing% is the percentage of all of a pitcher's pitches that batters swing at, while O-Swing% is the percentage of pitches hitters swing at outside the strike zone. Both of these numbers were markedly up from previous years. This also makes intuitive sense in relation to his increased first-pitch-strike percentage; hitters are going to chase more balls because Familia is getting ahead in the count more often. They are forced, or are at least more likely, to expand the zone.

The total Swing% is also up because of Familia's control in general. Major league teams are very thorough in their scouting reports, and word gets around quickly across the league. Familia has gained the reputation as a strike-thrower, so hitters are now more inclined to swing earlier in the count because they don't want to fall behind in the count, and because a walk and/or hitter's count no longer seems like such a likely outcome.

Contact% represents the percentage of opponents' swings in which they make contact, while SwStr% represents the percentage of pitches that resulted in a swing-and-miss. They relay similar information, and it makes sense that both indicate Familia generated more swings-and-misses in 2015.

Why? These are linked to the previous percentages. Familia gets ahead more often and causes more swings outside of the zone, and pitches outside of the zone naturally are harder to hit. Familia can also use his devastating off-speed pitches more when he's ahead, which generate a high percentage of whiffs as well.

It's important to note that there is not complete causation between the improved command and the increase in swinging strikes. Last season also saw the emergence of Familia's filthy splitter, which according to Brooks Baseball generated the highest whiff percentage out of all of his pitches in 2015. Nevertheless, the splitter is the off-speed pitch that is least known as a get-me-over pitch when behind in the count, so the fact that Familia was able to deploy his splitter so effectively in 2015 means that he was ahead in the count more often.

All of the plate discipline data besides the Zone% seems to indicate that Familia's better control was due to an improved approach rather than luck. It's not clear whether the low walk rate is sustainable or not—because who knows if the improved approach is sustainable? However, we can be reasonably certain that the new approach lends itself to better control. So if Familia pitches the way that he did in 2015—that is, he consistently gets ahead in the count—another low walk rate should follow.