Hey Cubs world, 

I've spent my initial time blogging here about the Cubs moves for 2025. However, sometimes its good to pause and reflect on general principles of baseball and how to build winning teams. 

In this post, I discuss a few basics of bullpen construction that fans often overlook. 

Beating Rival Teams: Targeted Bullpen Design

Wins Above Replacement is a generic approach to roster construction, and for that reason, can't be precise. If this were all that was necessary, a general manager could ignore all fundamentals and simply bid on the "Best" pitchers in rank order of how cost effective their contract is for producing wins. For example, one can look at the Dodgers and say - gee, Tanner Scott is worth whatever the market pays for him, regardless of which team he plays for. If this were true, pitchers would be bid on in rank over of their intrinsic value, and all pitching fundamentals could be ignored during roster construction.

There are several approaches to designing a roster that wins a division, which go above and beyond shopping for "wins". Ideally, a great team succeeds according to a more careful "fit" between the player and the rest of the 26 man roster, as well as the team's overall environment. In this short article, I'll outline these three main ways to improve past a simple "market rate" approach to assembling a winning bullpen. 

The Environmental Approach

One key task for the Cubs is to assemble a bullpen that plays well in the physical environment of their division, especially players who will succeed at Wrigley Field, but also at division rival fields. This analysis can involve digging into player statistics that indicate ballpark differences, day/night games, and so forth, to find out what independent variables predict wins against rivals. Typically, this approach is applied AFTER evaluating bullpen talent at market rates - in essence, looking for ways to beat the market price on the player because they play especially well in Cub-specific circumstances.  For example, Kyle Tucker is argued to be a near perfect fit to the Friendly Confines - his style of hitting and fielding both play exceptionally well there. However, he's also versatile enough as a player that he can win games at other divisional fields. 

Although this approach can work well for starting pitching or power hitting, it's not quite as important for bullpen construction. This is because pitchers who cover individual innings at a time have a more chaotic, fluctuating relationship to big environmental factors. Most importantly, bullpen pitchers are being systemically and methodically used by their coaching staff to deal with specific micro details, making it hard to tell exactly which environmental factors affect these small sample sizes. Put simply, a 10 or 20 pitch appearance doesn't produce enough data for us to distinguish environmental variables - did the player have sun in his eyes during Wrigley afternoons, or doesn't pitch well with grumpy coaches in April. Too many factors are at play simultaneously.  Therefore, the environmental approach can only "tweak" the expected player performance.   

The Bullpen Role Approach  

This is my favorite approach to fine tuning a bullpen: roles. It involves thinking of pitching and hitting as a complex game of scissors-rocks-paper, and each pitcher as a duelist deployed to duel with a few opponents at a time. Basically, each player's talents match up well in contests against a partial lineup of other players' styles of competition, while avoiding facing other players in the lineup that can exploit the pitchers' weaknesses. A bullpen is thus a giant Swiss army knife of tools, each designed to counterattack hitting styles of prominent rival players. A good bullpen has multiple answers to every problem, due to rest periods between pitching appearances. 

This simple example is a fairly popular perspective of bullpen construction, although you will see minor variants from team to team. I am listing the in the order of how popular it is for a team to specify this precise role, as opposed to perhaps other alternative roles in roster construction. The best set of arms consists of the following roles being covered. I am placing a Cubs bullpen name as a candidate for each role, followed by their current understudy who has options in the minors. You will notice that we have two ENTRE bullpens covered. Jed Hoyer eliminated all risk of being shorthanded; however, hoarding some of his best talent in the minors until July or later also involves a risk that they are underutilized for fear of injury. 

1) medium leverage swingman - every team knows who their workhorse bullpen arm is. Not necessarily their best player, but the one expected to get the most innings. A player with a high floor and a diverse skillset who can "handle" most styles of hitters better than average. 

Colin Rea, Cody Poteet

2) low leverage long reliever -usually a young, developmental starter who eats innings while playing from behind. Every team has at least one player who's being given a final shot to develop, and this is their last chance to win a bigger role. 

Keegan Thompson, Jordan Wicks

3) high leverage closer - proven veteran who is the best pitcher in the pen. Plays in close games. 

Ryan Pressly, (Porter Hodge is in the MLB)

4) low leverage closer - a pitcher with insane stuff but usually control problems. High risk to give up 1 run due to walks or solo dingers, low risk to give up more than 1 run due to high whiffs.  Plays in games with a larger victory margin than the main closer.  

Nate Pearson, Ethan Roberts

5) medium-to-high leverage right handed setup - a precision expert against most righties, and not expected to handle the toughest lefties

Porter Hodge, Ben Brown

6) medium-to-high leverage left handed setup - a precision expert against lefties, rarely allowed to face top right handed hitters

Caleb Thielbar. Luke Little

7)  medium leverage change of pace reliever - a unique pitcher who can disrupt and frustrate high-contact hitters with rare pitches, such as a submariner or knuckleballer. Most frequently plays the 7th inning and/or comes in early as a "plan b" to shut down opponent rallies.

Tyson Miller (extreme ride sweeper), Eli Morgan (extremely slow changeup)

8 ) high leverage power "hold" reliever - a high leverage early reliever who enters the game early to shut down power hitters. They lean on fastballs with elite velocity and strikeout rates. Basically, this is your top "hold" specialist against #3/#4/#5 power hitters in the order. 

Julian Merryweather, Jack Neely 

The Pitch Portfolio Approach

The most detailed and painstaking approach to advanced bullpen design looks at the fundamentals of each pitch, and how a pitcher combines pitches to produce a set of offerings. From this perspective, roles aren't as important as a direct comparison of pitch types and styles to hitting types and styles. The pitch portfolio approach looks directly at the advanced pitch metrics to predict "pitches that produce outs", and only secondarily bothers with a players' pitching "Role". Craig Counsell and Tom Hottovy both come from this school of thought: they simply match up the best pitches, at any given moment, with the greatest chance of producing outs. Obviously, pitchers need rest, so the most important metric is the net present value of "using a premium pitch" now as opposed to saving it for the next important situation.

This fine tuned approach to bullpen management is really only possible since the statcast era -- advanced pitching models/metrics and a reliance on obscure calculations. Every analytics driven team needs to balance pitch-to-bat matchups with less-than-perfect fit. This is where bottom dwelling baseball teams fall apart- they don't have enough diversity of pitches, or depth of players, to match up well and so they have to intentionally lose a certain number of games to win others. The main problem with the pitch-by-pitch approach is it under-emphasizes the human elements of the game, especially psychological makeup of particular players. This is a great approach to your "plan A" for each of the 162 games; however, the role of managers on a game day is to tweak and intervene and decide between plan b, c, d, etc, based on roles and environmental factors. 

From this third perspective, the Cubs are well prepared to face their opponents. They excel at pitching analytics. The biggest question mark for the 2025 season has to do with their success at filling roles with the right guys - particularly, having enough power pitching, enough left handed pitching talent, and an elite enough closer.