http://iscoresports.com/

I started scoring a game and only had 11 or 12 players on the roster. As the game went on, the coach substituted players with other players that I did not have on the roster when the game started. I was unable to add a player to the roster after the start of the game. I did go back to the team manager and enter them there, but I could not get them to appear in my list of players to choose from while I was within the game.

I couldn't do it either by tapping on the player in the field or at bat OR in the play by play. The only players that appeared on the roster were the original players I had listed.

This is a big problem, especially when I am scoring a game where I don't know the opposing team and players are substituted here and there.

Editing the Roster from Team Manager only adds players to the Roster.

During a game, to add a missing player, you should press Misc -> Show Starting Lineup, and add the player from there. This will add the player to the Lineup for the game and make them available to play in that game.

While you are on the Lineup screen, you should also tap Options, Copy Lineup -> Roster to also copy the newly added player back to the Team Roster as well for use in future games.

Yep, its an important distinction between Lineup and Roster.

When you start a game, the lineup is a snapshot of your roster at that moment. From that point on, any changes made to one, don't affect the other and vice-versa.

As FTM said, when you do make changes to your Lineup, if you want them to also be made to the Roster, than Copy Lineup -> Roster.