At the start of every football season, Sarah Clasen has the same conversation with parents in the stands. “Is that your daughter playing?” “Yes.” “I didn’t know girls could play.” They can — and her daughter, Sophia, does. Quite well, in fact. Sophia, 12, just finished her fifth year of tackle football. For all five years, she’s been the only girl playing tackle in the Oregon City Youth Football Association, and one of only a few dozen girls among the roughly