Wild Pitch and Passed Ball
The ball gets away from the catcher and runners move. Which of the two it is decides whose fault it was.
What it actually is. If a pitch gets past the catcher and a runner advances, the scorer charges it to somebody. A wild pitch means the pitch was too far off target for the catcher to handle with ordinary effort; a passed ball means he should have caught it. Both allow runners to advance and both can score a run, and the difference exists only in the book.
What somebody who knows the game gets out of it. The distinction has real consequences because runs scoring on a wild pitch are earned and runs scoring on a passed ball are not, so it moves ERA. It is also the most direct way blocking shows up as value: framing gets all the attention, but a catcher who blocks well saves free bases in exactly the situations where they are most expensive, with a man on third and fewer than two out. That is one of the components inside catcher defensive metrics and it is the part that is easiest to see from the stands.
The numbers worth knowing. A major league team allows roughly 55 to 70 wild pitches and 5 to 10 passed balls a season. The disparity is mostly scorer judgment: a modern breaking ball in the dirt is charged to the pitcher far more often than it once was.
What people get wrong about it. A wild pitch that gets past the catcher on a third strike is both a strikeout and a live ball, so the hitter can run to first. It is the single strangest common sequence in baseball: the pitcher is credited with a strikeout, the hitter is on base, and no error was made by anybody.
At Little League and travel ball. At youth level this is the dominant way runs score, full stop. A runner at third with a catcher who cannot block is a run more often than not, which is why stealing third is so aggressive at 10U and 11U and why blocking drills are worth more coaching minutes than throwing drills at that age.
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