"It's got to get better," Banister said after the Rangers lost for the fifth time in the last seven games.
The errors and walks were costly in the Astros' five-run seventh inning that ruined what to that point was an excellent outing by Cashner.
"We gave away five free passes off the mound with two hit batters and three walks, but the misplays are what really became challenging for us," Banister said. "When you only put two runs on the board it's really difficult when you give them those extra opportunities."
The Rangers led 2-1 going into the seventh before Cashner walked Alex Bregman to start the inning. Norichika Aoki followed with a ground ball to the left-side hole that shortstop Elvis Andrus backhanded and tried to make a jump-throw to second base. The ball got past second baseman Rougned Odor and the runners advanced to second and third.
"Leadoff walks will kill you," Banister said. "The misplays are challenging for us. However, we're on top of the defensive runs saved. The timing of the misplayed balls is really what causes the challenges, mixed in with the walks."
An error also cost the Rangers an unearned run after two outs in the first. Cashner hit Jose Altuve with a pitch and, with Carlos Correa at the plate, he immediately stole second. Correa then hit a high pop into shallow right-center. Right fielder Nomar Mazara had a long run and was able to get there. He just couldn't make a waist-high basket catch and the ball dropped for a run-scoring error.
"He was running and he looked like he had it," Banister said. "All of a sudden he moves his hands and it hits on the heel of his glove. Catchable ball."
Those are the hardest ones for Banister to take.
"Disappointing outing for us," Banister said. "It hard to get 30 outs. It presents a lot of challenges for us. Misplays are what's challenging but when you score only two runs, it makes it even tougher. We can't continue to give them extra opportunities."
T.R. Sullivan has covered the Rangers since 1989, and for MLB.com since 2006. Follow him on Twitter @Sullivan_Ranger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.