A passive construction emphasizes the person or thing which recieves the action of the verb, and de-emphasizes or even hides the agent (or actor) the person or thing that perfumes/does the action of the verb.
A passive sentence is normally constructed by placing first the person or thing which receives the action (here "the stalkers" or "the defenders"). This is followed by a conjugated form of the verb "to be" appropriate to the desired tense, which is followed by a past participle (here "gotten rid of" ) and an optional prepositional phrase, usually starting with "by".
The stalker was gotten rid of by Mary.
The stalker was gotten rid of.
"The stalker" was the object in the active form, and is now the subject. "the stalker" is what receives the action, here what is gotten rid of. "was" is a form of "to be". "gotten rid of" is a past participle of a verbal phrase "get rid of". "by Mary" is the optional prepositional phrase. If present, it tells who did the action. Mary is the agent here. (Sometimes also called "the actor" or "the performer".)
Many people advise against the use of the passive voice. It is seed to be weaker, more wordy, and generally poor writing. It can be all of those. But it can also be good writing.
The passive voice is used to emphasize the receiver of the action and decrease the importance of, or leave implicit, the agent. It is common, even required, in formal scientific writing, because that is supposed to be about what was done, not who did it. ("The testtube was opened" not "I opened the testtube".) It is properly used whenever the receiver is the point of the sentence, and the actor is incidental or unimportant.
The passive voice can be dishonestly used to obscure the agent. ("Many people were killed in the battle" rather than "Our army killed many people during the battle".) But when the agent is clear from context and the current focus should be on the receiver of the action (sometimes called "the patient" in older usage, a helpful term in this kind of analysis), then using passive voice can improve the writing.
Sentence 2 from the question:
Messi gets rid of the defenders easily and scores with his weak foot.
is a poor choice for the passive voice, because the emphasis is all on the actor, Messi , and the patient ("the defenders") is almost incidental. A passive construction would distort this.