Final answer:
The US pro league with the highest average ticket price is the NFL, due to its limited number of games and extensive fan base, which creates higher demand and pushes up prices compared to the NBA, MLB, and NHL.
Step-by-step explanation:
The US pro league with the highest average ticket price is the NFL (National Football League). The NFL often has higher average ticket prices due to the limited number of games (16 regular season games per team), which creates higher demand for each game. Moreover, the stadiums are generally larger, and the fan base is extensive, thus pushing up the average ticket price.
By comparison, other leagues like the NBA (National Basketball Association), MLB (Major League Baseball), and NHL (National Hockey League) have more games per season, which typically results in lower average ticket prices. However, prices can vary depending on the team, the city, and the market demand for a particular game.