Why doe Papa keep his broken leg a secret for Uncle Hammer?

From the text:

"I still don't want him to know 'bout this thing. If he knows I'm not on the railroad, he'll wanna know why not, and I don't want to risk that temper of his when he finds out what the Wallaces done."

Papa believes that Uncle Hammer will come to town all "wild and angry", that "he'll get himself hung."