What details in chapter 28 and 27 add to the mounting tension before Jem and Scout are attacked?

They heard an overweight negro and a middle aged homosexual playing "Just the Tip" behind a tree.

the dude is wrong they heard a underweight half white half black person riding in a car behind then while playing just the rip behind a lamp post

Thanks for the insightful answers. A student fell for it. Interesting conversation with the dean.