Dally tells Pony to look sick, to fool the cop.
Pony and the rest of the greasers have a definitive rumble with the Socs. The purpose of this rumble is for both sides to get even after what each side feels is an insult. Johnny killed Bob, but Johnny was attacked and is lying almost dead in a hospital as a result of an accident during a fire at the church he and Pony were hiding at.
Even though he too was injured in the church fire, Pony insists on going to the rumble for honor’s sake. He still wants to be part of the gang. He is shocked to see Dally there, since he was injured too. The greasers win, and Dally has a plan for getting them quickly to the hospital since they all look so bad.
"Look sick," Dally commanded. Till say I'm taking you to the hospital, which'll be truth enough."
I leaned against the cold glass of the window and tried to look sick, which wasn't too hard, feeling the way I did right then. (Ch. 9)
Dally tells the policeman that there was a motorcycle accident, and even gets them an escort to the hospital. He has warned Pony that Johnny does not look well, saying he was “gettin' worse” but asking for Pony.
When they get to the hospital, Johnny is indeed not doing well. It was probably a good thing they rushed. Johnny is dying. He has time to hear about the rumble, and tell Pony to “stay gold,” before he dies. Dally is overcome
"Damnit, Johnny ..." he begged, slamming one fist against the wall, hammering it to make it obey his will. "Oh, damnit, Johnny, don't die, please don't die..." (Ch. 9)
Johnny was very important to Dally. His death was a big blow. He flees when Johnny dies, unable to handle his emotions.
Dally’s ruse is another example of his creative interactions with authority figures. When Pony asks Dally how he got out of the hospital, he says he talked the nurse into “with Two-Bits switch” (Ch. 9). Earlier he did the same thing with a doctor to let them see Johnny, but that doctor said he was doing it because they were Johnny’s friends, not because of the knife. Dally feels desperate and scared because of Johnny’s condition, and that is why he is resorting to violence. It is the only way he knows of solving problems. At least with the cop he found a better way.