Zach Britton is the 2nd Best Pitcher in the American League

Begrudgingly, nearly everyone in baseball data science will say that they do not completely comprehend the value of relief pitching.  Often, you will hear how dominant relievers are incapable of starting.  That is pretty much true.  Often, you will hear that closers are not employed at the most consequential moments and often are given a clean slate when entering a game.  That is also true.  Often, you will hear how utterly confused analysts are when a reliever is paid big money, given a lot of years, or is acquired in exchange for multiple, notable prospects.  Often, you will hear how several teams put together dominant bullpens that are collections of spare, rubbish heap arms, which is also true.

If you simply read what most data analysts say, relief pitching continues to be overrated and dominant relievers are failed starters.  Of course, this statement seems a little silly, right?  How many failed starters are there each year at the MLB level?  At least 30.  Very few of them become dominant relievers let alone dependable middle relief arms.  There certainly is something more to it.  Relief arms tend to need one or two above average pitches and at least mediocre control.  The reality is that this is not a common thing among those failed starters.

Furthermore, maybe our ability to appreciate relievers with metrics like WAR simply measures their value inadequately.  In this post, I try to look at things from a couple different angles.  First, a somewhat traditional way looking at saves and blown saves.  To do this, I took the players with at least 60 save opportunities from 2013 to 2015 and selected the top 20 players.  I assumed replacement level closing was the average success rate of the bottom 5 of those top 20 closers.  This might actually be an overestimation simply because to rack up 60 save opportunities, you have to be an arm that a club has been devoted to.

What we find is that the bottom rung long term closer blows 6.5 games per 40 opportunities (84% success) every year.  A top five closer blows 3.1 games per 40 opportunities (92% success) every year.  That is a difference of 3.4 games.  A blow game does not mean a loss.  I would guess that a blown save in a closing situation may be a loss 70% of the time, which would mean that the bottom run closer would lose 2.4 more games per year.  At a cost per win of 7 MM, that would suggest on average that the elite closing arm is worth about 18 MM, which suggests that maybe closers are somewhat undervalued in the market.

Zach Britton is currently 37 for 37.  Based on the above, we would expect a bottom run closer to blow 5.92 games over that stretch.  If we depreciate those blown saves in a conversion over to losses, then we have 4.1 losses.  This would suggest that Britton has actually been worth over 4 wins so far this season.  This would nestle him right behind Corey Kluber's 4.3 fWAR for second in the AL among all pitchers.

Maybe the simplicity of looking only at save opportunities leaves your brain unmoved and your heart cold.  Well, we can dive into RE/24.  RE/24 looks at run expectancy before and after each event in a game and attributes those to a pitcher without consideration of anything other than run expectancy.  A starting pitcher can benefit simply by racking up successful innings and a reliever benefits by coming in to high leverage situations.  RE/24 often is most unfair to closers who tend to enter the game with a clean slate and somewhat indulgent to middle relievers who successfully enter games with men on base.

Anyway, I batched all starters together and all relievers together for each team, ran those variables along with RE/24 for team batting, and regressed all of that against team wins.  What I found is that relief RE/24 was 78% the value of starting pitcher RE/24, which is not accounted for with innings pitched.  I then took the RE/24 AL pitcher leaderboard and scaled down relief pitcher RE/24.  Next, I accounted for park factors in home and away stadiums as well as the defensive ability for each team.  What resulted was a RE/24(x) metric that I created.  Here is that leaderboard:

	Name	RE24(x)
1	Jose Quintana	27.0
2	Aaron Sanchez	25.3
3	J.A. Happ	22.8
4	Michael Fulmer	22.6
5	Chris Sale	19.4
6	Zach Britton	18.5
7	Cole Hamels	18.3
8	Justin Verlander	16.8
9	Marco Estrada	16.4
10	Danny Duffy	15.7
11	Chris Tillman	15.3
12	Corey Kluber	15.2

Britton shows up as sixth on this board.  He is not exactly challenging the leaders much, but he still shows he is in the conversation for Cy Young.

Of course, the argument might wind up being that while Britton excels at closing, so would several of the other pitchers on this board.  One way to look at that would be to see what exactly the impact of higher velocity might have on a pitcher's success.  An increase of 1 mph in general decrease a player's FIP by about 0.40.  Not all starters when pressed into relief roles enjoy an increase in velocity, but lets be kind and simply assume all starters would see a jump of 3 mph that suggests a FIP improvement of 1.20.

Our leaderboard using the players above would yield:

	xrFIP
1	Corey Kluber	1.81
2	Zach Britton	2.00
3	Aaron Sanchez	2.09
4	Danny Duffy	2.13
5	Jose Quintana	2.22
6	Michael Fulmer	2.26
7	Chris Sale	2.29
8	Cole Hamels	2.46
9	Justin Verlander	2.46
10	J.A. Happ	2.69
11	Marco Estrada	2.96
12	Chris Tillman	3.07

All of this tends to suggest that maybe all those who are upset with Zach Britton being in the Cy Young conversation might be relying a bit too heavily on unsteady data science analysis with respect to relief pitching.  Many analysts may be harping loudly about concepts and ideas that have been firmly in place within the sabermetric community for over a decade and may be forgetting that this is an area of baseball that has yet to firmly establish what exactly the value is of a closer in a definitive way.

Perhaps in the coming years, data science will find ways to measure relief pitching quality that has a more substantial methodology than we currently have.  Maybe that methodology will show that closing is not the realm of inadequate pitchers, but more perhaps something completely different.  The skill set needed to be an elite pitcher differs from those who start and maybe that means these are truly two different positions within the pitcher class instead of a first and second tier.

Or maybe not.