In which situation is obstruction called?

Obstruction is called when a player is physically interfered with as they attempt to advance to a base. This rule is in place to protect the runner's right to a fair opportunity to reach the next base without being hindered by a fielder who is not in possession of the ball. The call for obstruction underscores the importance of allowing a runner to advance unobstructed, which is fundamental to the integrity of the game.

In scenarios where a ball is thrown out of play, that situation pertains to other rules regarding dead balls and base advancements. Similarly, stepping out of the baseline is a separate violation that does not equate to obstruction but could be relevant in terms of a runner's legal path. Furthermore, when a runner is tagged out, this is simply a standard part of the game relating to outs and does not involve the concept of obstruction. Therefore, obstruction specifically focuses on the interference while a runner is attempting to advance, making the context of this call clearly aligned with player safety and competitive fairness.