BBM determines game length based on the number of outs generated by the visiting team's batters (and in rare cases when the SP goes longer than 9 innings).
If the number of outs is less than 30 it's a 9 inning game. 30-32 outs results in a 10 inning game, 33-35 11 innings and 36-38 12 innings.
BBM tries to get at least 26 outs from the teams in order to complete a game and when the starters don't generate enough outs it looks to the reserve players.
Note: Teams are not penalized if no reserve players are available.
Games will NOT go into extra innings if the visiting team's batters generated 30 outs but the home team is winning after the initial 9 innings.