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.