Poor Pop. He's sad and demoralized because his Knights aren't exactly wearing shining armor. They lose most of their games and Pop's slowly losing his mind.
"I shoulda been a farmer," Pop Fisher said bitterly. I shoulda farmed since the day I was born. […] I have that green thumb," he said huskily, "and I shoulda farmed instead of playing wet nurse to a last place, dead-to-the-neck team." (2.1)
We find out pretty quick what Pop's big problem is and why he's such a pessimist. First of all, the team's a mess. Also, he's got his issues with the Judge, who's actively working to make Pop's life miserable (see the Character Analysis of the Judge). That would probably be enough to turn anybody into a pessimist, but in this case there's more.
The more is "Fisher's Flop." It happened when Pop was a baseball player himself and was running the bases on the verge of winning the World Series for his team. And then, disaster struck. He tripped over his own feet, losing the game, the Series, and his dignity. He's never gotten over it.
Ever since then Pop has been a pretty cynical guy, believing that he has no chance at life and sure that he'll fail at everything. To make matters worse, he has a mysterious medical problem, athlete's foot of the hand. Weird, right? Nothing can cure it. Nothing, that is, except winning. When Roy appears on the team and the Knights win a few, Pop's hands miraculously clear up.
It's almost unbearable to see Pop get his hopes up for the team. He's not asking for much. Not a World Series, just the league championship. He's developed faith in Roy, but he knows it's a long shot:
Then to Roy's surprise, [Pop] said he never hoped to have a World Series flag. […] "It ain't in the cards for me—that's all. I am wise to admit it to myself. It took a long time, but I finally saw which way the arrow was pointing." (10.23)
But in possibly the saddest scene in the book, Pop tells Roy,
"Roy, I would give my whole life to win this game and take the pennant. Promise me that you'll go in there and do your damnedest."
"I will go in," Roy sighed. (10.25-10.26)
Sad, sad, sad. Roy had already agreed to help lose the game.
Our last glimpse of Pop is when he tells Roy to go in and keep the game alive for the team. After Roy's final strikeout, we never see Pop's reaction. Malamud leaves that to us to imagine, and we can't bring ourselves to do it.