I don't have your exact text version, because there is no flashback on page 85 of my text. I think you are referring to the flashback sequence in which Ponyboy explains why Johnny is the way that he is. Right before the flashback sequence, Cherry says this about Johnny:
"Johnny... he's been hurt bad sometime, hasn't he?" It was more of a statement than a question. "Hurt and scared."
Ponyboy then begins to tell Cherry what happened four months earlier. Ponyboy, Steve, and Soda were walking home from the DX station and noticed Johnny's blue-jeans jacket lying on the ground. That was already a bad sign, because Pony tells the reader that it was the only jacket that Johnny had. Steve looked at the jacket closely and noticed that there was a stain on the color. It was the color of rust. There was more of that stain on the grass as well. Uh oh.
The three boys began looking around and "heard a low moan and saw the dark motionless hump on the other side of the lot . . ." That sentence right there is quite gripping. The reader assumes it is Johnny, but also isn't sure because Hinton doesn't describe the shape as human. Just a motionless hump. It was in fact Johnny, and he had been beaten up so badly that Ponyboy almost threw up.
The rest of the Greaser gang arrives at this point, and Johnny regains consciousness. Between sobs and racking pain, Johnny eventually explains what had happened. A blue Mustang with four Socs in it had pulled up beside Johnny and beat him to a pulp. One of them had rings on his fingers, which cut Johnny up. Additionally they threatened him with all kinds of stuff (Hinton isn't specific here). The result of the entire event is that Johnny has been a nervous and jumpy guy ever since. He now carries a switchblade and claims that he will kill the next person who jumps him like that again.