First of all, if he is found guilty then there is no excuse. But as many have pointed out, nothing has been proven yet. And there's no reason why he should have disclosed this earlier. It's part of his private life--the only reason he's addressing it now is because the media found out.
On Friday, the Scottsdale Police Department said that Parker's BAC was .096 percent. In Arizona, a drivers are considered legally drunk if their blood alcohol level is .08 percent or higher.