From a Jeff Passan article on Zach Britton's sinker:
...one of [Britton's] coaches, Calvin Maduro, tried to teach him a cutter. He told Britton to dig his middle finger into the seams, rest his index finger alongside it and throw. The ball was supposed to move in against right-handed hitters. It dove a foot away.
"I don’t know what you’re doing," Maduro said. "Just keep doing it."