Rules

follow the rules
規則に従う

Example:
If you don't follow the rules, someone'll get hurt.
ルールを守らないと誰かがけがするよ。

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play by the rules
フェアプレーする

Example:
The game's no fun if you don't play by the rules.
フェアプレーしないと楽しくないよ。

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Comment:
You can use this expression even when it's not a game, in which case it means the same as follow the rules.

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bend the rules
規則を曲げる

Example:
I bend the rules sometimes when I have to.
必要な時はルールを曲げる。

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break the rules
規則を破る

Example:
Rules are meant to be broken.
ルールは破られるためにある。

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Comment:
No they're not, let's all follow the rules like good people...