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Your Ideal Bullpen: A final case study

A case study in bullpen specialization and depth.

Colorado Rockies v Seattle Mariners Photo by Otto Greule Jr/Getty Images

To wrap up this series on bullpen theory and the Mariners relief corps, I wanted to take a deeper look at two pitchers in particular: Tony Zych and Shae Simmons. In my article on Monday, I briefly mentioned my preference for bullpen organization. Rather than strictly defined roles like an eighth inning setup man or a hierarchy of pitchers based on situational leverage, I’d prefer to organize a bullpen around skill sets. And I think the group of relievers Jerry Dipoto has accumulated fits this theory perfectly.

In any given game, there are a wide array of situations that a relief pitcher could be thrown into—from starting an inning with none on and no out to entering the game with runners on and two outs. But a particular reliever may not be best suited for every situation. This is the underlying theory behind specialization. This is why left-handed relief specialists are so common throughout the game. But what if we took specialization past handedness matchups? What if we examined a pitcher’s skill set to determine the best possible use case and then filled a bullpen with pitchers who have complementary skill sets.

Before I get too deep into bullpen theory, let’s take a look at the two pitchers I mentioned. Tony Zych and Shae Simmons are remarkably similar in skill and in repertoire. I don’t think that’s a coincidence. Below you’ll find a table comparing the career stat lines for these two pitchers.

Player IP K% BB% GB% Zone% SwStr%
Player IP K% BB% GB% Zone% SwStr%
Shae Simmons 28 1/3 22.8% 9.7% 55.4% 45.4% 11.0%
Tony Zych 32 33.1% 9.6% 50.0% 45.9% 12.4%

The sample size isn’t the largest for either pitcher but what we do see are two pitchers with extremely similar skill sets. Zych has been able to generate a ridiculous amount of strikeouts but the rest of their stat lines look interchangeable. They both have a batted ball profile with above average ground ball rates, they’re pitching in the zone the same amount, and they’re inducing swinging strikes at nearly the same rate.

Both Zych and Simmons rely on two pitches, a fastball and a slider. Here’s a table comparing these two pitches from each of them.

Player/Pitch Frequency Velocity Horizonal Mov Vertical Mov
Player/Pitch Frequency Velocity Horizonal Mov Vertical Mov
Simmons FB 66.5% 96.0 mph -4.6 in 6.6 in
Zych FB 55.9% 96.5 mph -8.8 in 6.7 in
Simmons SL 24.3% 84.6 mph 7.5 in -2.3 in
Zych SL 41.4% 83.4 mph 7.2 in 2.2 in

Their repertoires are eerily similar but aren’t necessarily carbon copies of each other. Both fastballs sit around 96 mph with a healthy amount of sink to them. In fact, the vertical movement of these fastballs sit in the 95th percentile for all major league relievers in the PITCHf/x era. But Zych’s fastball has a ton of horizontal movement on it as well giving it some extra deceptiveness. Likewise, their sliders have a lot in common. The big difference is the amount of vertical movement Simmons gets on his slider which certainly helps him generate additional ground balls.

So why acquire a pitcher whose stat line and pitch repertoire looks pretty similar to another pitcher already in the organization? Well if you’re building a bullpen around skill sets, it’s important to build depth to have multiple iterations of those skill sets ready to plug in. Both Zych and Simmons have some injury concerns and if you’re counting on one of them to be a key piece in your bullpen, wouldn’t it be nice to have another sitting in the wings.

Among the other pitchers in the bullpen, Steve Cishek and Nick Vincent and Evan Scribner and Casey Fien have pretty similar profiles as well. They may not be mirror images like Zych and Simmons but they’re close enough and show the same kind of iterative skill sets that have been accumulated on the roster. What this does is give Jerry Dipoto and Scott Servais a plethora of options should the need arise. Each of these groupings fit a different role and possess a skill set that complement each other. One of the biggest reasons why Servais seemed to have trouble managing his bullpen last year was due to the lack of options he could turn to. Now, he has those options in abundance.