Phelps’ fastball velocity and variety are key to his success

After Carter Capps suffered a season ending UCL tear, the Miami Marlins’ bullpen looked to be in shambles.

Many wondered who would serve as the primary setup reliever to A.J. Ramos, especially after Mike Dunn landed on the disabled list in early April. Surprisingly, the bullpen, originally thought to be a weakness, has actually become a strength. One of the main reasons for its success is the emergence of David Phelps as an excellent setup man.

This season, Phelps has amassed an impressive 2.79 ERA with a 2.85 FIP. His 11.32 K/9 is well above the 8.64 K/9 league average for relief pitchers, and he has allowed less hard contact vs. league average (25.4% hard contact vs. a league average 30.5%). Those numbers are especially eye-popping because Phelps has spent his career as an average to below average starter/occasional relief pitcher. Advanced metrics tell us that Phelps is better than he ever has been before. Take a look at the table below to see for yourself.

Table 1. David Phelps advanced statistics 2012-2015 vs. 2016

When evaluating a pitcher, the trifecta of FIP, xFIP, tERA is usually considered the gold standard. As you can see, no matter what metric you choose, Phelps is simply pitching better this season than he ever has in the past. I included BABIP in this table because I found it interesting that it increased in 2016 compared to his career average. The fact that Phelps has produced the best statistical year of his career while simultaneously having a higher BABIP is support for the argument that Phelps has actually been good, rather than lucky.

How has Phelps pitched so well this season? The answer lies in his changing approach to hitters after a full time switch to reliever. First, as many starters experience when converting to relief duty, Phelps’ velocity has increased substantially. Just take a look at these velocity charts for Phelps’ four-seam and two-seam fastballs.

Figure 1. Velocity chart David Phelps’ four-seam fastball

Figure 2. Velocity chart David Phelps’ two-seam fastball

The average velocity has increased from 90.7 to 93.8 mph on Phelps’ four-seamed fastball, and from to 90.6 to 93.3 mph on Phelps’ two-seamed fastball. Phelps’ increase in velocity helps him two-fold. First, in general, faster pitches are more difficult for a batter to square up. Second, is that Phelps has increased the average velocity difference between his fastball and breaking pitches.

For example, the average velocity difference between Phelps’ fastball and changeup has increased from 7.7 mph to 8.8 mph, a full 1.1 mph difference. Therefore, with effective pitch sequencing, Phelps has increased the perceived velocity of his fastball. This is part of the overall theory of Effective Velocity, a term coined by baseball analyst Perry Husband. I won’t get too bogged down into the details, but Jason Turbow of SB Nation wrote an excellent long-form piece about Effective Velocity in 2014. In the article, Husband explains how differences in pitch speed can impact a hitter’s timing:

“Hitters are like sharks to blood. When they see two pitches in the same place and at same speed, they begin very quickly to be able to time them, and when they can time them, they attack. But that timing maxes out at about a 6-mph difference in pitch speeds."

Effective Velocity is impacted by pitch location, sequencing, and changes in pitch speed. In the above quote, Husband indicates that it is difficult for batters to time their swing when a pitcher alters the speed of subsequent pitches by over 6 mph. The difference between Phelps’ fastball and changeup is over 8 mph, meaning that with correct sequencing and location, Phelps is able to really throw off a hitter’s rhythm. This improvement in Effective Velocity alone would have helped Phelps this season, but incredibly he found another way to throw off hitters: by including a cutter more frequently in his pitch repertoire.

Phelps throws one of his three fastballs (four-seamed fastball, two-seamed fastball, or cutter) 82.3 % of the time. Here is the actual breakdown of his pitch usage and something I will talk about after you look at the figure: their horizontal movement.

Table 2. David Phelps’ fastball have similar velocity but different movement

Horizontal movement measures the amount of lateral movement a pitch has in inches, on average. A “negative” horizontal movement means that the ball runs towards right handed pitchers, positive means it runs away. What stands out in the above table is that Phelps’ fastballs have similar velocity but radically different horizontal movement. This makes the ball incredibly difficult to read coming out of his hand, as the pitches appear similar but in fact move very differently. Phelps’ fastball mix combined with his high Effective Velocity makes it very difficult to square up his pitches - and there is proof of this fact.

Let’s look at some sabermetric stats to see how difficult it is for hitters to square up Phelps’ fastballs. One way to analyze how difficult a pitch is to read is by looking at its foul per swing and whiff per swing percentages. Essentially, if a batter is having difficulty squaring up a pitch he is likely to whiff on it or foul it off. Here is a table at the whiff per swing and foul per swing percentages for each of Phelps’ fastballs.

Table 3. Foul per swing and whiff per swing percentage on Phelps’ fastballs

For Phelps’ four-seam fastball, its foul/swing percentage is 50.58% and its whiff/swing percentage is 28.49%. This means that batters only put Phelps’ fastball in play on 20.93% of their swings. That is staggering, especially since Phelps uses the four-seam fastball most frequently (37.7% of the time). When your favorite and most common pitch is so difficult to hit, you will be successful. To put that in perspective, the whiff/swing percentage on Aroldis Chapman’s four-seam fastball is 32.66%, and the foul/swing percentage is 45.16%. Therefore, batters put Chapman’s four-seam fastball in play on 22.18% of their swings. That means that batters put a higher percentage of Chapman’s four-seam fastballs in play than Phelps’ four-seam fastballs.

Even though we can’t fully attribute Phelps’ successful season to his increased Effective Velocity and three pitch fastball mix, it seems that these are definitely important factors in his improvement this year. Throwing off a hitter’s timing is key to a pitcher’s success, and Phelps’ has become a master at this skill. The proof is in the pudding, as by all measures, Phelps has had a fantastic year.

Data obtained from Brooks Baseball and Fangraphs.