In each of the following sentences, omission of a comma between a main clause and a subordinate clause muddles the meaning. Discussion after each example describes the complication, and a revision demonstrates how to eliminate ambiguity.
1. The candidate’s supporters and protesters championing his rival violently confronted each other in the city’s downtown district leading to multiple arrests.
The district did not lead to multiple arrests; the confrontation did. Separating the subordinate clause “leading to multiple arrests” from the main clause with a comma clarifies the relationship between cause and effect: “The candidate’s supporters and protesters championing his rival violently confronted each other in the city’s downtown district, leading to multiple arrests.”
2. The event did not turn violent as some media reports indicated.
“As some media reports indicated” is a subordinate clause to “The event did not turn violent,” so punctuation between the two segments of the sentence is required: “The event did not turn violent, as some media reports indicated.” (Without it, the sentence might be misread “The event did not turn as violent as some media reports indicated.”)
3. Who will work in the transition management office charged with executing the transition?
This sentence reads as if the transition management is one of two or more such departments, one of which has the stated task. But “charged with executing the transition” is a subordinate clause referring to the who of the subject, and inserting “which is” at the head of that clause makes the transition smoother: “Who will work in the transition management office, which is charged with executing the transition?”
4. The company has been our consulting partner of choice for the last four years having supported numerous projects during that time.
The phrase that begins with having is a subordinate clause, and subordinate clauses must be set off from main clauses with a comma: “The company has been our consulting partner of choice for the last four years, having supported numerous projects during that time.”
The following revision alters the emphasis somewhat but reads more smoothly: “The company, which has been our consulting partner of choice for the last four years, has supported numerous projects during that time.” Another option is “The company has been our consulting partner of choice for the last four years, and it has supported numerous projects during that time.”
5. They steal diamonds and bags of cash only to send them raining down from the sky.
Many writers refrain from inserting punctuation before a subordinate clause beginning with only, but this omission invites ambiguity—did they steal diamonds and bags of cash only, and not anything else?—so, for clarity, include it: “They steal diamonds and bags of cash, only to send them raining down from the sky.”
While I get it, that as you say, the district did not lead to multiple arrests; the confrontation did. Similarly, the candidate’s supporters and protesters were not championing his rival, only the protesters were. Don’t you think the supporters and protesters, both need to be separated figuratively (grammatically) as well as physically?
In another post, you define subordinate clause: “A subordinate clause, also called a dependent clause, consists of information to be combined with a main clause to form a single sentence. It resembles a main clause except for the presence of a subordinate conjunction or a relative pronoun, either of which renders it subordinate. Here are some guidelines about its use.” Accordingly, only sentence 2 contains an actual subordinate clause beginning with the subordinating conjunction “as.” Phases and clauses are different stuctures, so “The phrase that begins with ‘having’ is a subordinate clause” is confusing.
The German language has a very practical and logical way of handling this. ALL subordinate clauses are always set off by commas (or by one comma if it is at the end of a sentence). All of them, and no aping around.
Also, all of the “that” clauses begin with the word “dass”, and it is never omitted. Then, all “which” clauses begin with forms of “welch”, and it is never omitted.
[“Welch” and similar words have a lot of inflected forms: welch, welche, welcher, welches, welchem, welchen. These, I could do without, along with all of that grammatical gender stuff.]
I found all of that gender business for nouns to be a huge headache, and German has three genders. At least, in Spanish, French, and Italian, there are just two: masculine and feminine.
Still, the French Academy had to decided between “la microchip” and “le microchip”; and between “la bulldozier” and “le bulldozier”. Also, “bulldozier” is a four-syllable word in French!
In German, almost all modern words that are about neuter objects really are neuter: Auto (automobile), Golf (the sport), Radio, Radar, Flugzeug (airplane), Raumschiff (spaceship), das Vakuum.
But to the contrary “der Computer”, which is masculine. This is because almost all words that end in “er” are masculine.