Walker ran out the stand-up triple but the review, upon the request of Pirates manager Clint Hurdle, clearly showed the ball clanging off the glove of a fan attempting a catch well above the yellow line running across the top of the wall.
Walker's 10th homer of the season extended the Bucs' lead to 3-0.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. He can also be found on Twitter @Tom_Singer and on his podcast. This story was not subject to the approval of Major League Baseball or its clubs.