Generally people allowed in football field are the two team players and the match officiator which is the referee. Each team has 11 players and the two teams will have a total of 22 player , so if you the match officiator(referee) that makes 23 people. Another point of argument is the side line men each on each side, but they are not usually in the pitch, though they may step in to make a compliant but their job is withing the lines.