An -ing verb form (also called a gerund) is the form of a verb that ends in -ing: walking, writing, running. Sometimes, an -ing verb form introduces a fragment. When an -ing verb form starts what you think is a sentence, stop and check for a subject, a verb, and a complete thought.

You can correct this type of fragment either by adding whatever sentence elements are missing (usually a subject and a helping verb) or by connecting the fragment to the sentence before or after it. Usually, you will need to put a comma before or after the fragment to join it to the complete sentence.