Modem tapping is one kind of "hacking" for me. You can get banned for it.
It works like this: you pull out your internet connection wire (cat5) and wait couple secs and suddenly you will put it back in. Its like losing internet connection for some secs.
it will make everyone to freeze on your pc and you can kill them. Others will see you freezing. At the time when you are not connected to internet you are killing moving etc...When your connection works again then you see the kills who you killed while tapping. The others will not see your bullets or anything...you will walk from spot to spot.
It is just bad thing and i do not recommend you to do it.
And yes it does make you lag for the time while you are doing it.
Hope you got your answers from here

bad english right now woops
there are some other ways to do it. Like just pushing the reconnect button on your modem(every modem does not have it)
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If there is something i can do for you, then ask, i will try to