When Justine Siegal and Keith Stein envisioned the United States' first professional women's baseball league in 70 years, they wanted to do it right. So they examined the blueprints of successful women's leagues and studied the pitfalls that caused promising ventures to fail. Their research helped shape the Women's Professional Baseball League, launching next year, the latest in a wave of ventures looking to capitalize on the unprecedented rise in popularity of women's sports.