Which sentence is written correctly? maggie broke her leg, while jumping into the pool, and has to wear a cast for eight weeks. snow cones, a tasty treat, can be found in many delicious flavors. the musicians, performed their hit songs, at the weekend concert. mike, has lost 40 pounds, because he started eating healthy and running each day.

The sentence that is written correctly is:

Snow cones, a tasty treat, can be found in many delicious flavors.

This sentence is correct because the commas that introduce the phrase a tasty treat do not interrupt the grammatical structure as in the other sentences. In this case, the commas introduce this phrase as a postmodifier to the subject snow cones without interrupting the structure subject + predicate that is usually followed.

Meanwhile, in the rest of the sentences, there is a comma that either separates the subject from the predicate (incorrect) or that is just unnecessary, like in the first sentence.