Verbal are verb forms that do not act as verbs in a sentence but as nouns, adjectives or adverbs. There are three types: participial (It acts as an adjective), gerund (It acts as a noun), and infinitive (It acts as a noun, adjectives, or and adverbs).
In the sentence, "Skydiving" is a verbal gerund because it has a gerund (a verb root + "ing") and its purpose in the sentence is to act as a noun, as it refers to the sport or activity of jumping from an aircraft and performing acrobatic maneuvers in the air under free fall before landing by parachute.