Baselines are for runners, not fielders. If a fielder attempts to block the runner or block the path of a runner, it is considered obstruction. Obstruction is a judgement call by the umpire who must decide which player (runner or fielder) belongs in the contact spot at the time of contact.
Basically, obstruction, and some interference violations are about the right-of-way and which player is protected, runner or fielder. If the fielder is making play on a batted ball, he has the right-of-way.
If a fielder does not have the ball nor is he making a play on a ball, the runner has the right-of-way.
Obstruction is only called if the obstruction has an impact on the play. For instance, if a runner is obstructed but made it to an advance base anyway, the obstruction violation is ignored.
MUST KNOW: Obstruction doesn’t need contact to be called. The runner must simply be impeded from going to his base.
Umpire Tip: Intent is also an important consideration for umpires when judging obstruction. If the umpire sees the fielder made an attempt to get out of the way, even if the fielder still obstructed the runner, he should not be charged with obstruction.
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