Hit by Pitch
Get hit, take first, unless you leaned into it or swung at it.
What it actually is. A batter struck by a pitch that he did not swing at is awarded first base, as long as he made an attempt to avoid it or had no opportunity to. A pitch that hits him in the strike zone is a strike, not a hit by pitch, and a pitch that hits the bat first is a foul or a fair ball. The umpire has full discretion on whether the hitter tried to get out of the way.
What somebody who knows the game gets out of it. Getting hit is partly a skill, which sounds absurd until you see the same names at the top of the list every year. Hitters who crowd the plate to cover the outside corner accept inside contact as a cost of that coverage, and some wear body armour to make the trade cheaper. It is also the enforcement mechanism for baseball's unwritten rules, which is why intent is judged by umpires and why the warning system exists at all.
The numbers worth knowing. League wide, roughly one hit batsman per team per game in recent seasons, which is a modern high. A player getting hit 25 times in a season is near the league lead; the career record is over 280.
What people get wrong about it. A hit by pitch counts against on base percentage's denominator and in its numerator, so it helps OBP, but it is not an at bat and does not touch batting average. And if the pitch would have been a strike, the umpire is supposed to call a strike even though it hit him, which happens a few times a year and always produces an argument.
At Little League and travel ball. At youth level a hit batsman is mostly a fear problem rather than a strategy one. A ten year old hit once will step out on the next inside pitch for weeks, and the fix is drill work with soft balls rather than reassurance. This is one of the specific entries in the struggles list on this site, because it ends more youth careers than lack of ability does.
Batter's Eye: look up anything in baseball