The following sentence is missing punctuation: “The crowd upset by the delay began to chant loudly for the band to appear.” Explain where the error has occurred in this sentence and how it can be fixed.
Read the sentence aloud. Where do you naturally pause? Two commas are needed in this sentence to represent those pauses and help comprehension.
http://grammar.ccc.commnet.edu/grammar/commas.htm
See #4.