2 brief summary of the rule
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There is an optional rule in the DMG about hitting other creatures that are providing cover for something, on page 272.

It says that if your attack misses due to the cover provided and the attack roll was high enough to beat the AC of the creature providing the cover, you hit the covering creature instead.

There is indeed nothing in the PHB, as there is no default rule about hitting cover.

There is an optional rule in the DMG about hitting other creatures that are providing cover for something, on page 272.

There is indeed nothing in the PHB, as there is no default rule about hitting cover.

There is an optional rule in the DMG about hitting other creatures that are providing cover for something, on page 272.

It says that if your attack misses due to the cover provided and the attack roll was high enough to beat the AC of the creature providing the cover, you hit the covering creature instead.

There is indeed nothing in the PHB, as there is no default rule about hitting cover.

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source | link

There is an optional rule in the DMG about hitting other creatures that are providing cover for something, on page 272.

There is indeed nothing in the PHB, as there is no default rule about hitting cover.