Why does Atticus think Bob Ewell holds a grudge against judge Taylor? ch 27

From the text:

“You don’t know if Bob Ewell cut that screen, you don’t know who did it,” said Atticus. “But I can guess. I proved him a liar but John made him look like a fool. All the time Ewell was on the stand I couldn’t dare look at John and keep a straight face. John looked at him as if he were a three-legged chicken or a square egg. Don’t tell me judges don’t try to prejudice juries,” Atticus chuckled.