As they're walking home one night, Daniel and Nathan are suddenly attacked by a gang of about six or seven boys. The boys have already beaten up Nathan and clearly want to give him another good kicking. This is because Nathan's father is a tax collector, a hated occupation for a Jew at that time, as collecting taxes on behalf of the Romans was seen as a sign of complicity in their rule. The sins of the father have clearly been visited upon his innocent child.
Amazingly, given that he's a zealot and therefore violently opposed to Roman rule, Daniel is actually quite sympathetic to Nathan's plight. He understands that it's not his fault that his father is a tax collector. It is just such empathy that sets Daniel apart from other zealots like Rosh. In due course, Daniel's empathy will lead him to embrace the teachings of Jesus.
Daniel offers to walk Nathan home, and it's then that they are attacked. In the ensuing melee, Daniel is impressed at the way that Nathan handles himself. This young lad is definitely zealot material. Seizing his opportunity, Daniel asks Nathan if he'd like to use his fists for a good purpose. He wants to recruit the young man to the cause of zealotry.