As we enter the homestretch of the 2012 season, teams will be able to expand their rosters to 40 players beginning next week. Some September call-ups will have little fantasy or real world impact, but there are some top notch prospects that could help clubs as they make a push towards the playoffs or start to rebuild for 2013 and beyond. Savvy fantasy owners will need to keep an eye on these call-ups, many of whom offer both risk and reward. This week we look at possible impact call-ups in the NL.