Julie Stackhouse’s goal last Sunday was to win the Donna Half Marathon, a popular race that weaves through the coastal communities of Atlantic Beach and Neptune Beach east of Jacksonville, Florida. Stackhouse, a Jacksonville local, had good reason to think she could break the tape—she’s won the race twice in past years, and has notched victories in the marathon and relay, too. But even before she came face-to-face with an aggressive dog, Stackhouse knew she wasn’t going to win. She estimates her canine encounter slowed her down only around 45 seconds in total, but her impressive finishing time of 1:25:54—enough...