Rowdyism is also a noun for noisy, rough behaviour that can lead to fights, but the -ism ending makes it sound like a habit, a style, or a public problem — “rowdyism in the streets.” You meet it in newspapers, school rules, and old-fashioned complaints. It is rarer and stiffer than rowdiness. You would not usually say “his rowdyism” about one loud evening; you would say it about a pattern, or about a group. It still shows disapproval. Students can treat it as a heavier, more official cousin of rowdiness — same mess, more of a label.