For Ultimate leagues the game determines when to use long or short relief depending on the number of outs remaining in the game.
Initially, the game engine presumes that the game will be a 9-inning game. If the starting pitcher uses a start of more than 6 innings, then short relief will be used through 8 2/3 innings. The game then determines if extra innings are needed.
If the starting pitcher pitches 6 or fewer innings, then long relief will be used first.
If a reliever has a live relief appearance that night, it will be used. Otherwise an appearance will be pulled from their available stat pool.
Note: It is possible for long relief to be used even after short relief has been used. This occurs when a RP is still needed in the game, but there are no short relief appearances by anyone on the list. BBM will use those before it applies an AAA penalty for no pitchers available.
For Lightning and Express leagues, there is only one list of relievers, and they will pulled in ranking order until no more outs are needed to complete the game.
A reliever can only appear once in a game.