ASA test question

[IRISHMAFIA]

I really don't understand how anyone can actually read the rule and not come the correct answer

4.6.C: A substitute who enters the game without reporting is considered an unreported substitute

Since in the OP the unreported substitute has complete his/her turn at bat, subparagraph 3 applies:

When completing a turn at bat and is discovered
a. BEFORE the next pitch, legal or illegal
b. BEFORE the defense has left the field
c. BEFORE the umpires have left the field

According to OP, "c" applies so you go to the EFFECT:

1. The unreported substitute is officially in the game and ruled out. (B1 is out, nullifies the run)
2. All other outs that occur on this play stand (n/a in the OP)
3. All other runners will return to the base occupied at the time of the pitch (n/a in the OP)

BTW, the rule for 2015 reads the same as the rule for 2016