Unreported substitution, and then some

[Dakota]

WMB's analysis is the correct way to look at it. The open question is does U-trip provide a way that a single past error (S1 thinking they were B10) does not cascade into multiple penalties?

If any of these are BOO, then there is no violation anywhere, since once a pitch is thrown to the first player after the first BOO, the first BOO is now legal, and every player after that comes to bat in order. However, a player has to be IN the batting order to bat OUT of order.

S1 coming to bat has to be something other than BOO, since S1 is not in the batting order. There is no provision (I assume) for a separate penalty for using an EP after the lineup has been given to the umpire. Therefore, the only thing S1 can be is an unreported substitute. This means that B8 is no longer in the game, and the analysis then follows what WMB posted (B8 coming to bat is an illegal player, etc.)

The only thing I would add is whether the illegal players have to still be in the game when the protest is filed. S1 and B8 are not on base. Their infractions may (...may - I don't know U-trip rules) be moot at the time of the protest.