Sean Manaea is a professional and would likely be the first to say that his performance has been unacceptable for a team in a crucial playoff push. By every account he is a first class individual and we want him to succeed. He’s slated to start at least 5 more games this season. An uncomfortable question has to be asked: can the Padres afford to let Manaea make those 5 final starts?
Is Manaea just in a slump?
There is something wrong here. This type of off a cliff performance decline suggests more than just a slump. Reportedly Manaea left his August 16th start against the Marlins with a “tired arm” and skipped his subsequent bullpen session. He had his best start of the second half on August 21st against the feckless Nationals. But since then he has been lit up to the tune of 6 earned runs against KC and 8 earned runs against the D*dgers Saturday night. The brief interlude against the Nationals appears to have been the outlier performance as Manaea’s ERA was 5.40 in July and 7.88 in August. Through one game in September his ERA is 16.62 bringing his second half ERA to an astounding 8.36. This feels like more than your typical in-season variance. Coupled with the signs of fatigue, it feels as though there is truly something wrong in the realm of cumulative wear and tear or lingering injury underlying the woeful second half performance.
When asked if Manaea would be continuing to make starts for the Padres Bob Melvin offered a kind deflection: “I don’t make decisions like that after games. He’s performed really well for us… He hasn’t for a stretch here. But my confidence in him has not waned.” Melvin said.
This is a lovely statement from a supportive manager who understands how to protect the dignity of his players. But make no mistake, the Padres’ confidence in Manaea is shaken. The Padres have a 3 game lead on the Brewers and a half game edge on the Phillies to secure a Wild Card spot with only month of the season to go. It’s do or die time. Simply put, Manaea cannot continue to make his scheduled starts unless there is some reason to think his performance will return to that of the first half of the season. What are the Padres options here? If the Padres don’t think that will happen, they will most likely move Nick Martinez from the bullpen into Manaea’s rotation spot. The natural follow up question is: who will replace Martinez in the pen?
We’re going to do the math for the Padres here and show why, unless they have some secret sauce to fix Manaea, it’s actually an easy choice to bring Nick back into the rotation.
First our assumptions:
We are assuming that Manaea will continue to perform similarly to his second half so far
We are assuming that Nick Martinez will perform similarly to his prior performance this year in the starting role
We are assuming that Nick Martinez would have performed similarly to his prior performance in relief if he remained in the bullpen
The Breakdown
Note: We are going to use ERA as an approximation of pitching performance for purposes of comparison as this stat will be more familiar and intuitive to our readers than FIP, although the latter may be the truer indicator.
Nick Martinez has posted a 4.30 ERA on the season as a starter. Presuming he maintains that performance, and that Manaea would continue to post an 8.36 ERA were he to pitch, the upgrade from Manaea to Martinez would be expected to save the Padres (8.36 - 4.30) = 4.06 runs over a 9 inning stretch, an enormous sum. The question then is what will the downgrade from Martinez to the next best alternative cost the Padres in runs over a 9 inning stretch? Martinez has been stellar in relief this year posting a 1.70 ERA. It will likely be Pierce Johnson, who has pitched well so far in his minor league rehab stint, replacing Martinez in the bullpen1. Pierce Johnson has a lifetime ERA of 3.59. Presuming Johnson performs similarly to his lifetime average, the downgrade from Martinez to Johnson (1.70 - 3.59) = -1.89 runs per 9 innings. So doing the math, the Padres would prevent about 4.06 runs per 9 innings by replacing Manaea with Martinez, at the cost of allowing about 1.89 more runs per 9 innings by replacing Martinez with Johnson. That’s a net gain of (4.06 - 1.89) = 2.17 runs per 9 innings. That is an absolutely game changing difference, which makes this decision look like one of the easiest that there has ever been.
But it’s a little more complex than that because relievers do not pitch as many innings as starters. So it actually makes a little more sense to project out the total number of runs over the remainder of the season.
There is approximately 1 month left in the season which translates to about 5 Manaea starts that could be replaced by Martinez. Martinez averaged 5.5 innings per start this year. Multiplied over the presumed 5 remaining starts that would predict 27.5 innings from Martinez the rest of the way in the starter role which translates to 13.14 runs given up over that stretch if we presume he maintains his 4.30 ERA performance. If Manaea were to pitch those 27.5 innings and continue his 8.36 ERA second half performance that would predict giving up about 25.54 runs. So in terms of actual runs saved for the rest of the season the switch from Manaea to Martinez should save about (25.54 - 13.14) = 12.4 actual runs over the final month of the season. But if Martinez were to remain in the relief role he would not be pitching 27.5 innings. In the last month Martinez has made 10 relief appearance for a total of 12.33 innings pitched. Projecting Martinez’ 1.70 ERA relief performance over those 12.33 innings predicts 2.33 runs given up. If instead Pierce Johnson took those innings and performed to his career norm 3.59 ERA that would predict 4.92 runs given up over that stretch. Doing the math, replacing Manaea with Martinez is expected to save the Padres (25.54 - 13.14) = 12.4 runs the remainder of the season, and replacing Martinez with Pierce Johnson is expected to cost the Padres (2.33 - 4.92) = -2.59 runs the remainder of the season. The net (12.4 - 2.59) would be a savings of 9.81 runs over the remainder of the season. That translates to multiple extra wins.
We can take this a step further and calculate how bad Pierce Johnson (or whoever replaced Martinez in the pen) would have to perform over those 12.33 relief innings to make this tradeoff not worth it by simply adding the net runs saved to the projected runs allowed by Johnson and calculating the resulting ERA over those 12.33 innings. (4.92 + 9.81 runs)/(12.33 innings) = an ERA of 10.75. To summarize, if it is likely that Nick Martinez will carry a ~4.30 ERA over the final 5 starts of the season, whoever replaces him in the bullpen would have to post greater than a 10.75 ERA in the expected ~12.33 innings of relief appearances vacated by Martinez in order for the math to favor continuing to allow Manaea to pitch and keeping Martinez in the pen.2
There’s more nuance here of course. The Padres will have access to some information that we do not. If the Padres have reason to believe that Manaea’s woes can be mended with a brief hiatus and some extra work with the pitching coaches, a pivot to Martinez could be a temporary solution for a start or two. We have no way of knowing if this is possible, but clearly this would be a better outcome.
Managing a team with playoff aspirations requires facing down these uncomfortable questions. Baseball is about a lot more than math, and the Padres calculus must include the non-quantitative factors. But strictly by the numbers, to the extent past performance predicts future performance, Martinez should be taking the hill next Friday.
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We are choosing Pierce Johnson because he is a fairly likely candidate and it is very unlikely that a better candidate will materialize. But it doesn’t matter exactly who you think will replace Martinez, the point is that someone will, and that will be a downgrade. Our bullpen will get worse. The question is by how much?
Feel free to check our math. We went over it 3 times but it’s super late and we want to know if we made a mistake! You know where to find us: @Letters2AJ