At 42-51, and in the middle of selling season, we know the second half of 2013 for the Chicago Cubs isn't necessarily about wins and losses. We'll know by the end of the month what their roster will look like going forward -- and even then they might make some August deals. So instead of predicting a second half record, we'll keep our eyes on other things. Here are five things to look for in the second half: 1. Core guys: The second half will determine if some of the Cubs main guys will have taken the next step or are still stuck in neutral. At the head of that list is Starlin Castro. Unlike Anthony Rizzo, this isn’t Castro's first full year in the big leagues so advancement was expected. He finished the first half on a high note with hits in seven of eight games but his overall batting average (.243) tell his story. His on-base percentage will never be great unless he’s hitting for a high average. Some of his past problems are still there -- and that’s startling. Rizzo is starting to find his groove again as well but it’s yet to be determined if he’ll be a power guy with a high average or if he’ll simply be a home run hitter with high strikeout totals. He’s on pace for about 125 whiffs. Jeff Samardzija has to learn how to grind more. He’s been great in some of the bigger games but a season is full of less than dramatic ones. That’s when he has to keep his adrenaline going. All three have shown flashes but none have proven that 2013 is going to be a huge advancement year -- at least not yet.