To add to my last above, this is the interpretation I mentioned. The first is by Wendelstedt, and the second by Evans, who are two authors of pro rule interpretations:
"A runner that is running the entire distance outside of the running lane will not be protected if he interferes with a play at first base, even if it is in his last stride or step to the base. In order to be protected, this last step must be when he first exits the running lane" (recall that in order to exit, one must first be within)."
"A runner who has advanced the entire distance from home plate to first in fair territory making no effort to run within the lane is not extended the same leniency as the runner who runs in the lane as required and then cuts into fair territory near the base to touch it."
BTW, this interpretation is also endorsed by NCAA Softball. Here's a play from their case book. Note what they say at the end under (3):
I don't know if the same is true under softball sanctions that allow for a single-first base.
"A runner that is running the entire distance outside of the running lane will not be protected if he interferes with a play at first base, even if it is in his last stride or step to the base. In order to be protected, this last step must be when he first exits the running lane" (recall that in order to exit, one must first be within)."
"A runner who has advanced the entire distance from home plate to first in fair territory making no effort to run within the lane is not extended the same leniency as the runner who runs in the lane as required and then cuts into fair territory near the base to touch it."
BTW, this interpretation is also endorsed by NCAA Softball. Here's a play from their case book. Note what they say at the end under (3):
A.R. 12-46. A slap bunt results in the ball quickly being scooped up by the
catcher right in front of home plate. The catcher is ready to throw, but seeing
the batter-runner in her way with one or both feet out of the runner's lane, she
hesitates, eventually throwing accurately to first base but the throw:
(1) arrives late.
(2) hits the batter-runner two strides before the base.
(3) hits the batter-runner on her last stride before the base.
RULING: In (1), the batter-runner has not interfered if a fielder
does not throw or hesitates before throwing. For interference to
apply, the batter-runner must be guilty of interfering with the fielder
taking the throw at first base. If the fielder does not throw, hesitates
and then throws late, or makes an errant throw, it is not possible to
determine if the fielder taking the throw would have been interfered
with. For example, if the catcher throws the ball three feet above the
outstretched glove of the first baseman, the batter-runner will be safe
by virtue of the throwing error, not because of interference with the
first baseman taking a throw.
In (2) and (3) the batter-runner is out because she interfered with the
first baseman taking the throw at first base. In (3), the rule allows the
batter-runner to leave the lane on her last stride in order to touch first
base. If she has not been running in the runner's lane, this would not
apply since she can not leave the lane if she was not in the lane.
(Rule 12.17.1.5.2)
I don't know if the same is true under softball sanctions that allow for a single-first base.