The baseball rule book makes even the simplest things complicated! For example, many people believe that they understand the definition of the "baseline" on a baseball field. If you drew a straight line between each base, would that define the baseline? Believe it or not, that is NOT the case.
The baseline is determined by the position of a baserunner at the point that the defense initiates a play on him. For example, a baserunner makes a very wide turn while running past first base. While he is nearly in the rightfield grass, the defense begins to make a play on him. The baseline is then defined by imagining a straight line between the baserunner's position and the next base. If the runner moves three feet or more outside of that line while attempting to avoid a tag, he should be declared out.