You don't want the elbow locked. It doesn't promote the proper arm whip. Hillhouse preaches against locking the elbow. He wants a good elbow snap and then the wrist and fingers will naturally follow.
http://www.discussfastpitch.com/softball-pitching/11826-tricks-trade-review.html#post135284
http://www.discussfastpitch.com/softball-pitching/11826-tricks-trade-review.html#post135284
