Rays shortstop Asdrubal Cabrera doubled to lead off the bottom of the fourth inning against Rangers starter Ross Detwiler. The next batter, Tim Beckham, took a fastball high and outside for ball one. Catcher Robinson Chirinos popped up and fired to second, hoping to catch Cabrera too far off the second base bag. Second baseman Adam Rosales took the throw and applied the tag to Cabrera, who was deemed safe.
Cabrera shoved Rosales, which caused an argument and both benches to empty. Order was restored quickly, however, and no one was ejected. Marc Topkin of the Tampa Bay Times discerned that the issue arose when Rosales elbowed Cabrera as he slid back to second base. In my own interpretation, the elbow appeared to be inadvertent due to a loss of balance, not malicious. Cabrera likely thought Rosales was trying to push him off of the bag.
You can watch the benches empty with MLB.com video here.