Our rules reference is 5.09(a)(11), which reads in part:
In running the last half of the distance from home base to first base, while the ball is being fielded to first base, he runs outside (to the right of) the three-foot line, or inside (to the left of) the foul line, and in the umpire's judgment in so doing interferes with the fielder taking the throw at first base .....
When we said that you're not necessarily out for interference when running outside the running lane, we're calling attention to a few wrinkles in the rule. Here are the important points to remember when judging interference on 5.09(a)(11):
First, let's define the running lane: A three-foot-wide lane occupying the last half of the distance to first base. The lines marking the running lane are part of the running lane. That's important.
When is a runner out of the running lane? The batter-runner is out of the running lane when, during the last half of the distance to first base, one of the runner's feet (or both, for that matter) is entirely outside the running lane at the time that the interference potentially (but again, not necessarily) occurs.
A throw must be made. If the catcher, for example, comes up with a bunted ball and sets up to throw to first, but then stops and doesn't throw because the runner (in his view) is in the way, you cannot have interference. The fielder must make an attempt to throw to first.
The throw must be a catchable throw. Using the same example, if the catcher comes up with a bunted ball and then throws wild to first base because (in his view) the runner was in the way, you cannot have interference. The throw must be one that the first baseman has a reasonable chance (with ordinary effort) to catch.
Note carefully the language of the rule: "… interferes with the fielder taking the throw at first base." So umpire judgment rests on what's happening with the fielder at first base, not the fielder who is making the throw. This is a critical point and is often misunderstood. Points #3 and #4 rest on this point: That if there is interference, the interference is on the fielder receiving the ball at first base, not on the fielder throwing the ball from the vicinity of home plate. You will sometimes get managers arguing running lane interference mistakenly arguing that the fielder who threw the ball was upset by the runner's position outside the running lane. He's entirely mistaken with that line of argument.
There are two exceptions. There are two exceptions (wrinkles, really) in Rule 5.09(a)(11). First, the runner is permitted to leave the running lane to avoid a fielder attempting to field a batted ball. We know this already from what we've learned thus far about interference – that the fielder has the right of way in fielding a batted ball. Second, noticing that first base itself (the bag) is outside the running lane, the runner is permitted by rule to step out of the running lane for the purpose of touching first base.