Sporting Charts explains Defensive Indifference - DI

A defensive indifference scoring is at the sole discretion of the official scorer at each ballpark, and it is normally seen in the ninth inning when a game is out of hand. Typically, the team trailing and having a man on first base will advance the runner to second to avoid a force play or double play to end the game. It makes the defense work a little harder, depending on where the ball is hit. However, this ruling is occasionally seen in games as close as two runs. For example, let's say a team is down by two runs in the final inning and has a man on first with two outs. It makes sense to advance the man to second base to eliminate a simple force play ending the game. The defensive team will let him take second base because his run means nothing, since it is the batter who is the tying run.