After Jem and Scout are so viciously attacked, Atticus tells Heck Tate that Bob Ewell was "out of his mind" to do such a thing. Tate disagrees. He sees Ewell as a man who was totally depraved:
[Ewell] 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 . . . . He had guts enough to pester a poor colored woman, he had guts enough to pester Judge Taylor when he thought the house was empty, so do you think he'da met you to your face in daylight?
According to Heck Tate, Bob Ewell was a vicious coward who was worthless as a human being:
Mr. Finch, there's just some kind of men you have to shoot before you can say hidy to 'em. Even then, they ain't worth the bullet it takes to shoot 'em. Ewell 'as one of 'em.
Sheriff Tate was an excellent judge of character.
In Chapter 29, Sheriff Tate and Atticus discuss Bob Ewell's attack on Jem and Scout. Atticus comments that he believes Bob Ewell was simply out of his mind for attacking two innocent children, but Heck Tate disagrees. He tells Atticus that Bob Ewell was not out of his mind, but rather was just "mean as hell." Heck Tate believes Bob was a despicable individual who had enough liquor in him to attempt to murder two children. In Sheriff Tate's opinion, Bob Ewell was an evil man who deserved to be shot a long time ago. Bob's attempt to harm children was inevitable because he was such a coward. Atticus cannot comprehend what could possibly make a person want to kill two children, but Heck Tate assures him that Bob Ewell was simply a worthless, evil man.
Tate can judge character very well and she states that the reason for his crazed attack is his mind. Bob is a messed up person who views as revenge being the best dish. Even though they are simply children, Bob tries to kill them for revenge which also shows what kind of a low mannered person he truly is.