Well, “Sinbad” is the nickname that Paddy and his pals give to Paddy’s brother who becomes a sad, sad character in the story (forever taunted and tortured by pranks). In fact, it is one prank in particular that shows us how Sinbad is most portrayed as the subject of pranks and taunts: lighter fluid is forced into Sinbad’s mouth (and Paddy helps in this torture).
In truth, it is Sinbad’s brother Paddy who is the most responsible for maiming his brother permanently. Why? Igniting lighter fluid in a child’s mouth is not something easily recovered from. Sinbad is portrayed as being unable to stop the prank:
Sinbad’s lips had disappeared because he was pressing them shut so hard. Kevin pressed the fuel capsule against his mouth but it wouldn’t go in.
Note that Kevin is the first oppressor here, but then Paddy takes his turn and makes the torture really happen:
I pinched Sinbad’s arm; no good. This was terrible; in front of the others, I couldn’t sort out my little brother. I got the hair above his ear and pulled it up; I lifted him: I just wanted to hurt him. I held his nose. He gasped and Kevin shoved the capsule half-way into his mouth. Then Liam lit it with the match. It went like a dragon.
The ruthlessness of Paddy is absolutely deplorable. Pinching Sinbad’s arm is only the beginning. In my opinion, the statement that Paddy “couldn’t ‘sort out’ my little brother” and at that “in front of the others” is the worst possible thing Paddy can say. Paddy admits that he wants to hurt Sinbad for no reason, and hurt him badly. The key to the prank is holding Sinbad’s nose closed so he had to breathe out his mouth. This allows Kevin to shove the fuel inside and then Liam to light the match. Now Sinbad’s mouth and lips are burned beyond repair. Paddy is not troubled.
In conclusion, one could make the claim that Sinbad is Paddy’s meek foil. Where Paddy is someone who makes things happen, Sinbad is someone who allows things to happen to him. When fighting becomes severe in the book, Paddy makes up his mind to stop it (even if it means defending his brother, which was not something he would usually do).