Aybar diverted to his left, ran into fair territory, and ran into a fielder. Yet Aybar's original base path was clear and never was impeded. At the 1:15 mark of the video Aybar is in a line that will take him along the foul line to first base. That is his established line. It is also the required line per MLB rules. Aybar then diverts his line into fair territory and into the path of the fielders. He hits the fielder who does not have the ball. However:

(1) It was Aybar who changed his base path and ran into the fielder.

(2) The fielder Aybar hit was justifiably in the act of fielding the ball.

MLB rule 2.0 explains: OBSTRUCTION is the act of a fielder who, while not in possession of the ball and
not in the act of fielding the ball, impedes the progress of any runner.

http://m.angels.mlb.com/laa/video/v35760797/82814-angels-walk-off-in-protested-game