1. Missing Conjunction: There's no conjunction (like "and," "but," "or") connecting the two independent clauses: "very skilled cellist" and "people call him Big String?"
2. Comma Splice: The comma between "cellist" and "people" is incorrectly used to separate two independent clauses.
3. Question Mark Misuse: The question mark at the end is confusing, as the sentence is not a direct question.
Here are some ways to fix the sentence:
Option 1 (Using a conjunction): A very skilled cellist, and people call him Big String.
Option 2 (Using a semicolon): A very skilled cellist; people call him Big String.
Option 3 (Making it two sentences): He is a very skilled cellist. People call him Big String.
Option 4 (Combining with a prepositional phrase): A very skilled cellist, known by many as Big String.
Choose the option that best suits the context and tone you want to convey.