Let me start from the beginning - just a little bit, basically Mr. Ewell was angry at Atticus for what he'd said at trial about his daughter - that in the end he decided to attack Jem and Scout in the woods.
BUT, Jem heroically got Scout out of the way - risking his own life. To make matters worse, though, poor Jem did end up with a broken arm.
I hope all is well and you pass! (: Good luck, rockstar! If you have any follow up questions, let me know! This book is still fairly fresh in my mind! (: