There are positional hierarchies in sports (a la 2nd baseman vs SS).
What are safeties?
Few great players start out at safety. They may be a LB that is too small, but fast. They may be a CB that isn't super fast or lacks good swivel in their hips. Maybe they're too tall to be agile enough play CB. There's many things they could start out as, but a deficiency is likely behind their move to safety. Hell, they could be a great 2-way player in HS, and they play safety as a sort of breather on defense.
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2nd basemen are failed shortstops. Period. Their range keeps them on the field, but their arm moved them off SS. LF and RFers are positions, but they lack the range of a CF. The RF has a good arm, so the LF is the least toolsy player in the OF.
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Same with guards vs tackles in football. A great blocker that lacks length plays inside. Tackles need to be a certain height with a certain wingspan.
I'm sure there's a bunch of nuanced reasons hockey players play certain positions, too, but I don't know shit about it.
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I thought all of this was common knowledge. Maybe not.