What can you infer about the boy's potential for violence based on his first words?

If you are referring to what the boy, Roger, says at the beginning of the story, I would argue that his first words betray his fear more than his potential for violence.

When Roger tries to snatch Mrs. Luella Bates Washington Jones' purse, he gets a rude awakening. Because the purse is heavier than he anticipated, he falls as he simultaneously tries to gain his balance and to prepare to flee. After he falls on his back, Mrs. Jones kicks him in the behind and hoists him up by his shirt front. The text tells us that she then proceeds to shake Roger "until his teeth rattled."

It is Mrs. Jones who speaks first. She orders Roger to pick up her purse and to hand it to her. He complies without a word. Then she demands to know whether he is ashamed of himself, to which Roger replies, "Yes’m." Next, Mrs. Jones asks Roger the reason for his actions. Roger meekly replies, “I didn’t aim to.” In the story, he doesn't tell her why he wants to steal her purse until later. His next words are also noteworthy.

“If I turn you loose, will you run?” asked the woman. “Yes’m,” said the boy. “Then I won’t turn you loose,” said the woman. She did not release him. “I’m very sorry, lady, I’m sorry,” whispered the boy.

Roger's first words betray his fear and his embarrassment at having been caught. He also seems genuinely ashamed for his actions. Roger seems more intent upon what he can get from Mrs. Jones' purse than on hurting her. So, from his first words, we can infer that Roger demonstrates little potential for violence.