BTW, since you asked about the Toronto Maple Leafs. Their official story is that they were named after the Maple Leaf Regiment which fought in World War I. Since Maple Leaf is a proper noun, you pluralize it by adding s at the end. Like Mr. and Mrs. Child are the Childs, not the Children. But there doesn't seem to be any evidence that there ever was a Maple Leaf Regiment. The truth is that the hockey club most certainly got their name from a minor league baseball team of the same name (like the New York Giants in the NFL copied the name of the baseball team that now resides in San Francisco).
According to baseball reference the team that became the baseball Toronto Maple Leafs started in 1895 in the Eastern League. The Eastern League at the time was a class-A league, which was one level below the majors (the other classifications being class-B, class-C, and class-D). They first took the name the Maple Leafs in 1899, probably because they were the team with a maple leaf on their jersey. Team names weren't very creative then. It was the color of your socks, the color of your jerseys, or something equally mundane. They had a maple leaf on their jersey, so they were the Maple Leafs (c.f. with the Cincinnati Reds, the Boston Red Sox (originally the Red Stockings) and the Chicago White Sox (ditto) today). In 1912, the AA-class was created (once again at the time the highest level below the majors), and the Eastern League changed its name to the International League and moved up to AA.
In 1927, when the Toronto St. Patricks hockey club were sold to Conn Smythe and looking for a new name, the baseball Maple Leafs were riding high, having won the lL pennant the year before. The baseball team was owned by Lawrence "Lol" Solman, Solman was also managing director of the Mutual Street Arena, the premier hockey rink in Toronto at that time. What better way for Smythe to ingratiate himself with arena management (and ride the coattails of another successful sports team) than to change his hockey team to the Maple Leafs? The hockey club won 11 Stanley Cup championships over the next 40 years, and nowadays probably don't want to admit that at one time they were less popular than a minor league baseball team. Hence the "Maple Leaf Regiment" story.
The International League moved up to AAA when that was created in 1946. Those Maple Leafs saw a decline in attendance in the mid 50s, and while they won 3 IL pennants in the 60s, the writing was on the wall when they were sold to a businessman in 1967 who moved the team to Louisville and made them the Colonels. The team only lasted there a couple of years before being moved to Pawtucket and becoming the Pawtucket Red Sox. Toronto got a major league team only a few years later when the Blue Jays were founded in 1977.