Romero had been throwing across his body, with a lot of his momentum heading toward the third-base line instead of directly to home plate. That has stopped Romero from properly following through on his delivery and creates problems with location.
"I think over the last couple of years he has gotten himself into a position where it's difficult for him to repeat pitches where his initial stride is going," Walker said. "We're trying to get him cleaner to home plate, more of a straight line, which frees up his arm a little bit.
"It can be a gradual thing over time, or something that isn't easily seen to the naked eye in the short term, but over the long term you notice differences in the delivery from a couple of years ago to now, and that's when you need to address it."
Romero has always thrown across his body, but he began doing it in a more pronounced way last season. The coaching staff made its discovery while going through video from previous seasons and have since made the necessary changes.
The 28-year-old Romero has made the adjustments off dry ground and in the bullpen but is still in the process of attempting to carry that work into game situations. That was the goal for his last outing, against Detroit, but as Romero's competitive nature took over he reverted back to his old ways instead of sticking with the game plan.
That's one of the main reasons why Romero's next start will come in a Minor League game Thursday. The hope is that Romero will settle into a scenario where he can focus on working with the new mechanics as opposed to trying to retire every hitter he faces.
"You just have to let your athleticism go out there and let that take over," Romero said. "The bullpen and whenever I'm on my own with no ball, I exaggerate it and try to do it as perfect as I can.
"Obviously during the game in the middle of the competition you're going to shift over a little bit, but the more you get the muscle memory under control I think the better off I'm going to be."
Romero also has adjusted where he sets up on the rubber for each pitch. He now positions himself in the middle of the rubber as opposed to the first-base side. With his across-the-body throwing motion, the previous positioning made it difficult to locate fastballs on the inner part of the plate to right-handed hitters.
The goal for all of this is to put Romero in a better position to throw with consistent command. That's something he struggled with last season as he issued a career-high 105 walks in 181 innings of work.
"It's really the direction of his hips and where he's going out of his initial break in his stride," Walker said. "I want him taking those hips directly to home plate. When guys go across their body, they typically take their hips in the direction opposite of where they're throwing the ball.
"It's not a huge adjustment for him, or else we wouldn't be doing it right now. It's an adjustment we think he can make, he's confident he can make, and it'll only help him out being more consistent."