Replay Review and the Challenge
A manager gets one challenge, keeps it if he is right, and cannot use it on the one call people most want reviewed.
What it actually is. A manager may challenge one reviewable call per game and retains the challenge if the call is overturned. From the eighth inning onward the crew chief can also initiate a review. Reviewable calls include force plays, tag plays, fair or foul in the outfield, catch or trap in the outfield, home run boundary calls and baserunning errors. Balls and strikes are not reviewable.
What somebody who knows the game gets out of it. Replay changed on field behavior in ways the rule did not intend. Middle infielders stopped the phantom tag at second, catchers stopped blocking the plate before they had the ball, and runners stopped popping up off the bag, because a tag maintained on a runner whose foot momentarily lifts is now an out that can be found on camera. Those are small things that add up, and they are a good example of how a review rule reshapes technique rather than just correcting mistakes.
The numbers worth knowing. Around half of all challenges are overturned, which is a sign managers challenge only when they are reasonably sure. A review takes a minute or two on average.
What people get wrong about it. The standard is clear and convincing evidence, so a call that is too close to tell stands as called. That is why a replay that looks fifty fifty on television confirms the call rather than reversing it, and why fans experience the standard as inconsistent when it is being applied exactly as written.
At Little League and travel ball. There is no replay at any youth level and there will not be. The relevant youth version is the appeal and the protest: some rulings can be protested to a tournament director because they are misapplications of a rule, and judgment calls never can. Knowing that distinction is what makes an argument at a travel field worth having or not.
Batter's Eye: look up anything in baseball