Indoor Softball uses a modified set of rules, the details vary according to league and venue. For the last few years we have played in the Tuesday night Manchester Indoor Softball League using the rules described below.
Each batter receives only one pitch - if it's a strike or foul ball the batter is out, if it's a ball the batter gets a walk. Teams bat for a set amount of time rather than for a set number of outs. If a batted ball hits the roof (the actual roof - not the net over the pitch) the batter is out and the ball is dead. Scoring is similar to outdoors, one run per runner who crosses home plate. When a batter hits the far wall for a Home Run the batter, and any base runners, don't physically run the bases, they all just leave the pitch, with one run credited for each of them. A batter can be caught out even if the ball has previously hit a wall or netting.
Indoor Softball is played on a much smaller pitch than the outdoor version and that means a different pitch layout. A ball that hits the floor is either fair or foul, a ball that hits a wall on the full may be a Home Run, Out, or Play On (note that a batter can be caught out even if the ball has first hit a side wall or the net below the roof).