We don't know much about Judge Banner, but what we do know isn't good. He's a lying, cheating skinflint who will bet against his own team to make a buck. The owner of the New York Knights, he sees the team as his personal piggy bank, nothing more than a business, and doesn't care about winning if he can make money losing.
When Roy shows up in the dugout the first day saying he'd gotten a contract for $3,000, Pop tells him that he's been tricked:
"It was for a five thousand minimum but the Judge said I already missed one-third of the season."
Pop burst into scornful laughter. "Sure, but that entitles you to be about thirty-three hundred. Just like that godawful deadbeat. He'd skin his dead father if he could get into the grave." (2.47)
Later when Roy asks for a raise to a decent salary, the Judge intimidates him into giving up and levies a fine on Roy for a uniform that Bump destroyed.
The Judge is also hell-bent on running Pop out of his job. He doesn't care if the team loses every game. In fact, he's happy when they lose, because that means that Pop might finally give up and retire:
"[L]ast season when the Judge bought into the club and then took advantage of Pop's financial necessity to get hold of ten per cent of his shares and make himself the majority stockholder, was our worst season. We ended up in the sewer and this year it looks like a repeat."
"The Judge is trying to push Pop out of his job although he has a contract to manage for life—that's what the Judge had to promise to get that ten per cent of stock. Anyway, he's been trying everything he can think of to make things tough for Pop. He has by his sly ways forced all sorts of trades on us which make money all right but hurt the team." (2.184-85)
Malamud gives the Judge no redeeming qualities. He's a completely unscrupulous and evil guy. He gets a serious beating from Roy at the end of the novel, but he's really already won.