aOBP% subtracts out HR to reveal how often these guys are actually on base for the guys behind them.
So, Hernandez actually increases the PA with guys on base for the batters behind him (even if it's just slightly), while batting Santana 4th would lead to at least a 40% increase in plate appearances he'd have with runners on base. Admittedly, Hernandez would create about 15 extra outs on the year, but I think that is more than offset by putting Santana is a position to hit with far more runners on base.
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You have to look at multiple seasons. A single season's numbers have proven to be a poor predictor of future performance.
I'm very impressed at the time you're taking to put together those charts. Are you not going to work for some reason?
What I'm struggling with is that (if I understand you correctly), if Santana would have hit 4 home runs and 30 singles last year instead of 34 home runs he would have been a better leadoff hitter because his aOBP would have been higher since he got on base 30 more times "for the guys behind him".
OK, but is it better to hit a home run and have a guaranteed run or to hit a single and be on base so you can possibly be driven in?
As for the 15 extra outs per season Hernandez makes, I'm not sure about that. Last year Hernandez had 667 PA's and made 445 outs. He got on base 222 times, hence his .333 OBP. Santana had 686 PA's and made 414 outs. So Hernandez made 31 more outs in 19 fewer at-bats. Give him the 19 additional at-bats which equates to 13 more outs and he ends up making 44 more outs than Santana, not 15.
Unless you're counting Santana's home runs as outs because he didn't get on base.
That’s 44 more times Santana would be on base with Hosey, Lindor and Reyes coming up, meaning more runs would be scored with Santana hitting leadoff than Hernandez. There would be fewer solo home runs hit by those guys.
But on the other hand, Santana hit 20 more home runs than Hernandez and it’s reasonable to say that if he were hitting leadoff more of those home runs would be solo shots than if he were hitting, say, 4th. So it’s a trade-off.
I don’t think you can demonstrate the team would score more runs with Hernandez leading off than Santana. I can’t prove it’s the other way, though, although I think it is.
If it’s the same either way then I want the better hitter getting more at-bats. Moving Santana from cleanup to leadoff gives him 52 more PA's based on your 2019 PA chart. Dropping Hernandez from 1st to 7th gives him 102 fewer PA's. Reyes would move up a spot, giving him 20 more PA's and whoever hits 6th would get a few more. Basically Hernandez loses 102 PA’s and Santana and Reyes get most of them. I’m pretty happy with that.
I feel we’re talking apples and oranges here since you insist on tossing out the 2019 numbers for both players and going with either their career numbers or their 2016-18 numbers. These guys both had close to 700 PA’s last year. That's a lot of data to throw away, especially since it's the most recent data. But if we can’t agree on that I guess we just won’t agree, which is OK.