There are several places in "Casey at the Bat" where you might get the sense that Mudville fans need to take an anger management course. They are a pretty angry, aggressive bunch. In fact, the poem contains lots of fairly rough, violent imagery that ends up giving the poem kind of a foreboding tone in some places. Hey Mudville, why so angry?
Lines 33-36: The crowd doesn't take strike one very well. The description of the stands "black with people" gives us the impression of a dark, angry, faceless mob. Kind of scary, right? Thayer uses a simile to describe the sound of the crowd: the angry "roar" sounds "like the beating of the storm waves on a stern and distant shore." The word "beating" seems pretty ominous, especially if you happen to be the umpire. Someone actually calls for the poor umpire to be killed. That seems like a bit much, right? No sportsmanship trophies for the Mudville fans. They're just too angry.
Lines 45-46: Previously, Casey had been the voice of calm and reason amidst the rabid Mudville supporters: "With a smile of Christian charity great Casey's visage shone; / He stilled the rising tumult." But now, it looks like the crowds' anger and violent tendencies have affected Casey. He doesn't seem like the image of cool control anymore: "his teeth are clinched in hate; He pounds with cruel violence his bat upon the plate." That bat pounding the plate kind of mirrors those waves beating the shore from line 34. It looks like Casey has gone over to the dark side. Say it ain't so, Casey.