Oddsmakers are constantly mindful of the physical and situational aspects of sports matchups, but they are also aware of public perception and market realities. As a result, oddsmakers shade the line, or move the spread around, to account for fan favorites and achieve nearly equal bets for each team in the matchup.
There are many factors that play into public perception.
For example, the public has a large recency bias. Most bettors are going to look back on the last game each team played and the result of that last game will disproportionately impact their bet. If Team Apple crushed the last team they played, even more bettors are likely to bet on Team Apple.
The public is additionally influenced by teams with historical roots or emotional stories. Think back to the 2016 World Series: the Chicago Cubs versus the Cleveland Indians in a best-of-seven matchup. The Cubs had not won a World Series since 1908 and there was an overwhelming desire in large swaths of the public to do away with the Curse of the Billy Goat. Bookmakers needed to shade the line to account for public emotion here.
Additionally, Chicago is a much larger geographic area with a far wider media market. Many more people in the United States have or feel a personal connection to Chicago than to Cleveland. This type of geographic discrepancy is also something bookmakers take into account.
This type of geographic issue comes up in many areas and leagues. For example, New York teams receive a disproportionate amount of bets for their teams. New York is both a “big money state” (as in, there are a lot of individuals with significant disposable income to apply to betting) and a highly populated area, where many people feel personally connected to New York’s sports teams.
If a sportsbook has a game on its books with a New York team versus a smaller market team, such as a team from Florida, they will need to shade their line in order to influence more individuals to bet on the Florida team and achieve equal betting action.