How much contact is usually allowed in officiated game?

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Asking a realistic question in realistic situations.

Basketball is a contact sports, and while it's easy to spot illegal contacts on players with the ball, it's quite difficult to spot illegal off-ball contacts unless it's too obvious.

So my question is in an officiated game, how much illegal contact is usually allowed, for example off ball plays, typically for rebounds because that is where most of the dirty work happens.

The Rule clearly states you cannot displace, restrict, hand/body check opponents but truth is these things happen quite often and many times go uncalled until things get too hot. So how much is too much?

We don't see this too often in the NBA because they have higher field goal % & players are less motivated to hustle & box out hard for rebounds, but in semi-pro or amateur leagues, hustling is much more intense & frequent, so does illegal contacts, and also fist fights.