Without regard to how it should be done, isn't that what the book says?

Tru has raised an excellent point. R1 and R2, base umpire in the C position behind F6. On an caught infield line drive where the runners have left the base before the batted ball is touched, the book says the PU makes the call at 2B? I assure you this gets called by every BU partner I've ever worked with. Semi-applicable MLB video example: Bryant's line-drive double play | MLB.com

While this IS a live-ball appeal, it's not a "tag-up & advance" appeal, which is probably what Andy was referring to.

I pregame out of this for the call at third. Never even thought of the call at 2nd mattering. I tried to pre-game out of this with our UIC and she told me I should just go with the assignments in the book.

But take this a step further, if you are following the book and the appeal is executed by tagging the runner while off the bag. Whose call? It's indistinguishable from the first play. (It's an out whether an appeal or not.)

Well, actually the mechanics you are citing are for tag up responsibilities. IMO, the attempt to double off R1 on a line drive, is the first play in the infield and belongs to the BU

If the throw is to the fielder who takes it by tagging the bag, how can you think of it as anything besides the appeal of the tag play? I mean it's obvious to everyone in the park that she left early. That said, that's my pregame: let's treat any tag up that occurs that looks like a play and use the play mechanics instead of the appeal mechanics. I think it makes total sense I just don't think it's what the book says.

Logically, this makes sense to me. By extension, if the line drive or fly ball caught in the outfield is thrown to an infielder in an attempt to double off R1, is this, too, the first play in the infield?

And just to advocate the devil's position on this... FP game w/ R1 on 2B. BU in "C". Batter hits a sharp line drive to F7 who fields it on one hop and throws to 3B attempting to retire R1 who is advancing. Is this "first play in the infield"?

My training has me busting inside towards 1B where my responsibility is picking up the BR. PU should have the play @ 3B. Yah?

One of the most often misstated (and missed on the field) mechanics. First play in the infield relates to batted balls that are first fielded by an infielder, making what NFHS calls an initial play. Any ball first fielded by an outfielder is either fly ball coverage, or base hit coverage (even if a force play to 3rd by F7!!).

At 3rd, even if first play, from the OF is PU.

So we are in violent agreement. :D

Where did I state it wasn't an appeal play?

How can a ball fielded by an OF be considered the "first throw in the infield"?

It's not, obviously. I'll go back to (FP):

With runners on first and second and less than 2 outs, who should make the live ball appeal call on a runner leaving too early at second base?

The mechanic says the PU is responsible for the tag up on the runner on 2B.

And it also says the BU is responsible for any play at 2B.

Appeal play: A play on a rule violation on which an umpire may not make a decision until requested by a manager, coach or player.

Play: An attempt by a defensive player to retire an offensive player. A pitch is not considered a play except as it relates to an appeal.

I'll propose that a live ball appeal at second base that originated from a throw from an outfielder is a "play" and should be called by the BU.

If play has ceased, ball returned to F1 in the circle, and then the defense properly appeals, this would result in a dead ball appeal and I'd suggest that this call belongs to the PU.

All appeal plays are plays but not all plays are appeal plays :D.

I appreciate where you're trying to get with this and I think it's basically right as to result.

But if the runner at 2nd does tag but just leaves a touch before the ball is caught, that's not meant to be taken by the BU even if that appeal is the first play. Now if everybody in the park saw her leave early and the only question is whether the ball beat her to the bag, we definitely have a call that should belong to the BU. But I don't think that distinction (nor the one you propose) is actually what the mechanics say (as a result of inartful drafting). The mechanics just say that some tag up appeals belong to the PU. And many times they assign the play that would correspond to that appeal to the BU.

Speaking ASA, it should be noted that there is an inconsistency as some of the sections of the mechanics refer to coverage on a "fly ball to the outfield" while others note "fly ball coverage". IMO, that is an indication the references are to balls to the outfield.

AFA balls in the infield, there is no assignment of any type of appeal responsibilities outside of the normal play & base assignments.

Apparently this has been changed in the 2017 USA Umpire Manual. It's noted on page 66, under the fly ball coverage. PU now has tag up at 2B. That section is in grey highlight so they did indicate that this is a change.

Nice. I think this makes more sense.