Nobody expected an expansion team to become one of the biggest stories in the WNBA this season. The Golden State Valkyries have changed that narrative in a hurry.CBS Sports released its midseason report cards this week, and one of the biggest winners wasn't the defending champion Las Vegas Aces or the Minnesota Lynx. Instead, it was the WNBA's newest franchise, which earned an impressive A grade after exceeding virtually every preseason expectation.It's another reminder that the Valkyries' remarkable first season is becoming impossible to ignore.Golden State's defense has become its identityThe Valkyries enter the second half of the season with a 15-7 record and one of the league's stingiest defenses.CBS Sports pointed to that defensive identity as the biggest reason behind the team's succ