For any game, practice, drop-in, you can set lines. In hockey, for example, you can set your 1st, 2nd, 3rd forward lines, 1st line of Defense, 2nd Line of Defense, Primary Goalie and Backup Goalie, Left Wings, Centers, and Right Wings.
If a person marks themselves out of an event, then they are automagically removed from the lineup.
To set the lines, simply click on the position, and a list of available players will be shown along with their preferential position. Players are only shown if they’ve marked themselves as ATTENDING for the event.