The Astros and Rangers rivalry hasn't existed, as much as Bud Selig wanted to claim it to be when he touted it as a reason to move the Astros to the American League. Both teams haven't been good at the same time, especially with the Astros not holding up their end of the bargain for the most part since 2005. That probably won't be the case going forward.
Mark July 18, 2015 as the start of a rivalry between the two teams. At the start of the 9th inning, Rangers second baseman Rougned Odor was at-bat. Josh Fields entered the game to pitch. Fields, the umpire, and Astros catcher Hank Conger were ready to start.
Odor had other plans. Odor didn't step into the box after a look or two from Conger. Conger appears to have said something to Odor about getting into the box. Odor wouldn't have any of it and the two started to jaw.
Rangers designated hitter Prince Fielder rushed in and appeared to be playing piece maker stepping between the two players -- he shoved Conger out of the way.
The benches cleared. A.J. Hinch and Fielder seem to come toe-to-toe during the scrum. At one point, Fielder shoves Hinch.
At which point, Rangers manager Jeff Banister stormed in. Hinch and Bansiter were screaming at one another, Hinch being held back by an umpire.
There were no ejections after the benches clearing event, but a rivalry may finally be born.