
Who hit the most HRs while batting in the leadoff (#1) slot in the batting order?
What is the numerical arc of the leaders over the 1-9 BOP sequence?

We'll try to answer all of those questions as we proceed through the batting order.
In the #1 slot, it won't come as much of a surprise to discover that baseball's greatest leadoff hitter, Rickey Henderson, is the leader in #1 slot HRs by a wide margin. That gap between him and Alfonso Soriano might close a bit...frankly, we don't see very many more PA's in the #1 slot in Soriano's future.
Soriano, by the way, holds the record for the most HRs hit by a leadoff hitter, with 39, set in 2006. That broke his previous record--38--which he'd set in 2002. All in all, Soriano holds four of the top six slots for homers by leadoff men. There are a total of 14 player seasons where the #1 slot hitter has managed to hit 30 or more HRs in a single season.
In the #2 BOP, we see (despite the claims of Neil Paine) the emerging acceptance of the primordial sabermetric principle that this lineup slot not continue to be sacrificed to slap hitters. One of the reasons why the #2 slot is still a bit under-represnted in terms of homers is that its function in the batting order (to the extent that such things actually make a difference, that is...) has always been a mixed one. It wasn't until the early 80s when teams began to recognize that a #2 hitter need not have a power profile that resembles a guy with the uniform number "1/8" on his back.

You might be surprised to see Eddie Mathews in twelfth place on the #2 BOP list. How and when did a 500+ HR guy wind up hitting in the #2 slot? We can't be sure about the "how" (aside from Eddie's manager writing his name on the lineup card), but we can pinpoint the "when." It was 1959: Mathews batted second for the Braves in 145 games that season. He also set the record for the most HRs by a #2 hitter for a single season, with 46. All in all, Eddie hit those 85 HRs in the #2 slot in just 376 games.
Trailing Mathews is Ryne Sandberg, who hit 40 HRs while batting in the #2 slot in 1990. To show how this lightweight sabermetric principle has taken hold, we see that nine of the top twelve leaders in most single-season HRs hit by #2 hitters are from 1990 or later; five of them have occurred since the year 2000.
We'll be back with more HR by BOPs very soon. As we always say...stay tuned.