What does Heck Tate give as the reason for the attack?

Atticus believed that Bob was crazy. Heck believed he wasn't man enough to face Atticus, but that he was drunk enough to attack his children.

“Don’t like to contradict you, Mr. Finch—wasn’t crazy, mean as hell. Low-down skunk with enough liquor in him to make him brave enough to kill children. He’d never have met you face to face.”