Why does Darry not want Ponyboy to fight?

Darry doesn't want Ponyboy to fight for a few different reasons. One, he's recently been in the hospital. Two, he's too worked up.

"Yeah," Darry said with a proud grin. "You fight real good for a kid your size. But you were in shape before. You've lost weight and you don't look so great, kid. You're tensed up too much."

i love that story, but darry doesnt want ponyboy to get hurt.