Are the Padres really worse against lefties?

In the debate over who should be the Game 1 starter, there were two different viewpoints. The first is that Kwang Hyun-Kim has been a better pitcher than Jack Flaherty this year, so he should start Game 1. The second is that Jack Flaherty IS a better pitcher than Kim so he should start Game 1 and 9 starts shouldn’t change that. Some people who agree with the latter viewpoint have come around to Kim because of one central fact: the Padres appear to be a worse team against lefties than against righties.

But I couldn’t accept that. Because I thought about who was on their team, and who primarily received plate appearances, and well, I was struggling to figure out how exactly this is a team configured to be worse against lefties. It’s not a lefty-heavy lineup. Their three best hitters are all right-handed. If my assumption of their lineup is correct, they have five right-handed hitters, one switch hitter, and three left-handed hitters. Platoons exist for a reason, so it stands to reason that, well having just three left-handed hitters would not exactly make a team susceptible to left-handed pitchers. They’re outnumbered!

So, the question I must ask now is: if they are not in fact worse against left-handed pitchers, why have they been worse against left-handed pitchers this season? There are two specific ways this can be true. The first is that a right-handed hitter who should be better against lefties isn’t, or at least his numbers are not better. This is easily my best route. Unless the hitter has shown a history of being worse against lefties, the assumption is that his 2020 numbers are a fluke. The other is that the Padres have used left-handed hitters that they probably wouldn’t in a playoff series, or at least they wouldn’t start these hitters.

Let’s start with the former. Whose numbers are out of whack? Wil Myers is not the answer. He has a 176 wRC+ against left-handed pitchers this season, in comparison with a 143 wRC+ against right-handed pitchers. This is actually a bigger disparity than his career, but he’s still better against LHP in his career: 117 wRC+ versus 107 wRC+. How about Manny Machado? Nope, his numbers are as expected: 154 wRC+ against LHP, 146 against RHP. This is pretty much the difference in his career splits too. This is two of the nine hitters who are actually better against LHP both in 2020 and career.

Our first real clue that, hmm, maybe these numbers are not trustworthy, comes in the form of Fernando Tatis Jr. Against LHP, he has a 113 wRC+. Against RHP, he has a 163 wRC+. I could give you sample size reasons for why this is not to be trusted, but well Tatis Jr. made my job very easy. Because he obliterated lefties in 2019. I’ll put it this way: despite the fact that he’s way worse against LHP in 2020 and despite the fact that his career is just two half seasons, his career numbers against LHP are clearly better than when he faces right-handed pitchers. For his career, he has a 172 wRC+ against LHP, and 142 against RHP.

Tatis Jr. has the most PAs on the team, so this takes care of quite a bit of the difference by itself I imagine. Their presumptive choice for catcher against Kim also has numbers that I can’t imagine are his true splits. Right-handed Austin Nola has a 154 wRC+ against RHP, 54 wRC+ against LHP. He didn’t play all year for the Padres, so I checked his Padres specific numbers against LHP, and I checked each game he played in. Against lefties, he went 3-25 with 3 BBs with a double. This is a pure fluke. He had a 135 wRC+ against left-handed batters last year, 103 wRC+ against right-handed batters. He only has two seasons.

So I’ve covered four of the five right-handed batters. Career-wise, three of them are better against left-handed pitchers, including a guy with drastically worse numbers against LHP this year. Nola was much better against LHP last year, much worse this year. In lieu of an adequate sample size, I must conclude he’s better against LHP since that’s how the vast, vast majority of MLB players work. That leaves one more right-handed batter, Tommy Pham, who has not played most of the year, but has 35 total PAs against lefties. He’s a 145 wRC+ career hitter against LHP, 120 wRC+ against RHP. I would show you 2020, but 35 PAs. Aw what the hell you probably think I’m hiding worse numbers. I’m not. He has a 161 wRC+ against LHP in those 35 PAs.

Jurickson Profar is marginally worse against LHP for his career (91 versus 87) and pretty much the same disparity is present in 2020 (113 versus 108). You’ll get no argument from me that Eric Hosmer, Jake Cronenworth, and Trent Grisham are all worse against left-handed pitchers. Hosmer’s got the only reliable sample of the three - (79 versus 121), but lefties as a whole tend to be worse against left-handed pitchers.

It’s also worth pointing out that on Roster Resource, three of the four players on the bench are left-handed. They would not be a factor against Kim because they would not play. The fourth is Jorge Mateo, who won’t play either, but is right-handed. So that’s three guys whose numbers factor into the teams against LHP, but don’t apply for a start against Kim.

So I think I’ve more or less established that the Padres seem to follow the basic rule of thumb with splits, which is that right-handed batters are better against left-handed pitchers, and left-handed batters are better against right-handed pitchers. But do the relative weaknesses of the three left-handed batters outweight the five right-handed batters? Well, LHB are in fact worse against LHP than RHB are against RHP. Mostly because to survive in this league, you have to be able to hit right-handed pitching and if RHB had the same disparity that LHB did, there would be way less offense in the MLB.

Back in 2014, Tom Tango, Mitchel Lichtman and Andrew Dolphin wrote “The Book: Playing the Percentages in Baseball.” In the book, they noted that the average platoon split for a left-handed batter was a difference of .027 points of wOBA, while a right-handed batter’s difference was .017. A few players have worthwhile sample sizes that I’ll just directly take their difference in wOBA at face value: Hosmer, Myers, and Machado. Profar, being a switch hitter, requires much less of a sample, so I’m taking him at face value. The rest, I’m going with The Book averages.

Machado (.015), Myers (.015), and Profar (.008) are all fairly simple and in line with what to expect, but Hosmer is very far off the expectation with .063 difference. Okay I lied. What am I really supposed to do is regress the career numbers against 1,000 PAs of the average, I just had no clue Hosmer would be so far off the average. Not going to go into details, but here’s the formula if you want to use it from the source itself. Hosmer has a large sample, so his expected numbers is still 51 worse. That’s going to make a dent. The rest I’ll use the averages.

The left-handed hitters plus Profar combine for a whopping 113 worse. The right-handers by comparison are just 81 better. Which basically means by using a left-handed pitcher, the Padres lineup is 32 points of wOBA worse than if they faced faced a right-handed pitcher. So technically, yes starting Kim makes the Padres lineup worse. Most of that is one guy, but they are in fact worse.

So there’s your justification. I still can’t really help but feel that you’re basically starting a lefty so that Eric Hosmer can turn into Pete Kozma, but that five other guys get better, but I set the rules so I’m forced to concede. If you wanted to take this point further, and I do not, the next question would be is the difference of Flaherty and Kim large enough to overcome those 32 points of wOBA.

How much is 32 points of wOBA (points or runs? I have no idea). Somewhat helpfully, Trent Grisham has 30 points of wOBA difference in his numbers, so we can have some idea of what this means for wRC+. He has a 126 wRC+ against righties, 106 wRC+ against lefties. The Padres as a team have a 115 wRC+, which basically means if we apply the wOBA difference, the Cards can either face a 121 wRC+ (against RHP), or a 101 wRC+.

I wish I had rest of season projections for the next part, but I do not. I know Flaherty’s performance will lower Flaherty’s expected performance from his original 3.39 FIP projection. Similarly, Kim’s original projected FIP is probably lower than 4.30 now. But I don’t think the difference will be as much as you’d think. Kim isn’t striking anybody out and he has a higher BB/9 than ZiPS thought too. Flaherty meanwhile has a 3.42 xFIP.

I’ll be honest. I went into this thinking that the difference in handedness would probably favor the right-handed batters of the Padres, but I did not take into account how truly dire Hosmer is against lefties. If you make him into a normal lefty against lefties, the difference in wOBA is just 8, and if it’s that small of a difference, I think you just go with the better pitcher. But a 20 point difference in wRC+? That’s not nothing. So I came in with a preconceived conclusion and was proven wrong. I’m glad the Cardinals aren’t stupid, for this decision at least.