This summary is not the rule. The rule text controls.
Here's what this rule means in plain terms.
If police want to arrest someone, they normally have to knock and announce who they are and why they're there before entering. This rule says that if the person refuses to let them in, or blocks them from entering, officers are allowed to force their way in. This applies to homes, buildings, cars, boats, planes, or any other place where the person being arrested is located.
There's also an important exception. If announcing themselves first would put the arrest at risk (for example, giving the person time to grab a weapon, destroy evidence, or escape), officers don't have to announce their presence before entering. They can go straight to breaking in if needed.
In short, this rule gives police the legal power to force entry when making an arrest, as long as they either announce themselves first or have a good reason not to. It balances the need for effective arrests with some protection against officers barging in without any warning at all.