Chicago Cubs' third baseman Matt Duffy (back) said his goal is to return around the All-Star break. He's been sidelined since May 25 with a lower back strain. The 30-year-old was on the verge of being able to play in rehab games but his back didn't respond well after a vigorous pre-game workout. "I was trying too hard to force it," said Duffy. "The way it behaved it was, I would be fine for the most part one day, I could do whatever I was doing, and then the following day, it just wouldn't feel...