Answer:
A sentence fragment is a group of words used as a sentence that lacks a crucial element that makes it an incomplete thought
A comma splice on the other hand is a mistake when two independent clauses are spliced together with only a comma.
The part which best describes Jerry's place among the boys is the following: They shouted cheerful greetings at him; and then, as he preserved his nervous, uncomprehending smile, they understood that he was a foreigner strayed from his own beach, and they proceeded to forget him.