This is the person in the sportsbook responsible for establishing the original and subsequent betting lines for an event. This person may also be known as a handicapper.
The linemaker is one of the most important people in any sports betting operation. The best linemakers work for big casinos and sportsbooks and make plenty of money doing it. The job is important because their ability to set a line that attracts a balanced amount of action on each side of the line is directly related to the profitability of the sportsbook. Linemakers and handicappers use all sorts of information to create and move their lines, including: past betting lines, past wagers, the team or competitors recent win/loss streaks, overall winning percentage of the teams involved, etc. Needless to say, a good linemaker or handicapper spends a lot of time ensuring they make the right line, and unless something unexpected happens, they are usually right on target.