Dropped third strike question

[Paul L]

New Official Baseball Rules, rule 6.09(b):
The batter becomes a runner when --
...
(b) The third strike called by the umpire is not caught, providing (1) first base is unoccupied, or (2) first base is occupied with two out;
Rule 6.09(b) Comment: A batter who does not realize his situation on a third strike not caught, and who is not in the process of running to first base, shall be declared out once he leaves the dirt circle surrounding home plate.

I believe the dirt circle surrounding home plate is 13 feet in radius around the tip of home plate. (It's hard to read the MLB diagram 1 in rule 3.01.)