Marine Corps veteran Nate Walker was unable to sit through a major league baseball game for years after he returned from Afghanistan. Haunted by the time he spent clearing explosives along military routes, he worried what others at the game might have hidden inside their bags or under their sweatshirts. That changed when he got his service dog, Yazhi, who accompanied him to Coors Field in May to see the Colorado Rockies play the Los Angeles Dodgers. "I haven't been to a stadium with that many people since I've been home," the 26-year-old Denver resident said.