There is no set number. Some track meets have a limit to the number of entries but I have never heard of any team having a set number of people. the only reason a college team may have a limit is if a coach sets one.
There should be 22 players on the field 11 players from each side are allowed.
There are 9 people on the field in a game of softball + reserves.
Traditionally, there are nine players on the field... the batter is not included, because he is not a 'field' player/position. There are three outfielders, three basemen, a shortstop, a pitcher and a catcher... that equals 9.
11 on-field players
All the players are official whether they're on the field or not.