The Base Path and the Running Lane
A runner's path is defined by where he is, not by a line painted on the field.
What it actually is. A runner's base path is the direct line between him and the base he is going to, established at the moment a fielder tries to tag him. He may run more than three feet either side of that line only if he is avoiding a fielder making a play on a batted ball. Separately, there is a painted running lane in the last forty five feet to first base, and a batter running to first must be inside it or risk being called out for interference on a throw.
What somebody who knows the game gets out of it. The base path being defined at the moment of the tag rather than as a fixed line is the detail that makes rundowns work the way they do, and it is the rule most often misunderstood by people who have played the game for years. It means a runner who is standing still ten feet inside the infield grass has that as his base path, and a defense that expects him to run on the chalk is going to miss him.
The numbers worth knowing. Three feet either side, forty five feet of running lane to first, and the lane is three feet wide with the line itself in fair territory.
What people get wrong about it. There is no painted baseline between the bases, and the chalk running down the first and third base sides is the foul line, not the base path. Those two lines are frequently confused, and a runner sprinting on the outside of the foul line down to first is exactly where the rules want him.
At Little League and travel ball. The running lane rule is called inconsistently at youth level and is worth teaching anyway, because a young hitter who runs inside the line on a bunt is going to be called out eventually and will not know why. The out of the baseline rule shows up mostly on rundowns, where the practical youth coaching is simple: make the runner commit, and run him back toward the base he came from.
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