From the benches, black with people, there went up a muffled roar, Like the beating of the storm-waves on a stern and distant shore. "Kill him! Kill the umpire!" shouted some one on the stand; And it's likely they'd have killed him had not Casey raised his hand.
Things start to take kind of an ugly turn in stanza 9. The imagery turns pretty dark and violent.
The bleachers ("benches") are "black with people"—presumably because they're packed to tightly together they look like one dark blob of humanity together. That doesn't give us a very happy, sunny, day at the ballpark feeling.
Storm-waves are "beating" the poor defenseless shore, and now the fans want to kill the umpire. Can't we all just share some Cracker Jack and get along? Aren't sports supposed to be fun? (Heh—yeah, we remember PE. Fun's got nothing to do with it.)
Thayer uses a simile to describe the crowd noise: it's "like" the sound of giant storm-waves crashing on a rocky shore.
The description of these "storm-waves," "beating" the "stern" shore gives us the impression of something other than a beach holiday. We aren't picturing sunny Hawaii and white sandy beaches. These waves and this shore seem much more foreboding.
After the first "Kill him" we think for a moment that the crowd has turned on Casey. But as is often the case when our heroes fail, we look for someplace else to lay the blame. Who's easy to blame when things aren't going well for your team? Yup—referees and umpires, that's who.
In this case, the crowd becomes murderously enraged with the umpire and "some one on the stand" calls for the umpire's death. It's all pretty dramatic for a small town baseball game, but these Mudville fans take their baseball very seriously.
That phrase "on the stand" er… stands out (see what we did there?). The preposition "in" would be a more expected choice than "on." We usually talk about people being "in" the bleachers, or "in" the stands.
What does the phrase "on the stand" make you think of? Come on, we know you've watched some Law and Order. In courtrooms people are described as being "on" the witness "stand." Hmm—so why the weird pronoun choice, Ernest?
Well, when we read the stanza's last line, it kind of makes sense. The situation becomes a loose metaphor for justice. Casey is the judge and he puts a halt to the murderous rage and comes to the defense of justice. The crowd is like a crazed jury, ready to pass judgment on the poor umpire and send him to his death. Luckily, the voice of reason and justice (Casey) won't let that happen. So maybe he's not such a bad guy after all. Let's keep reading to find out…