OAKLAND – At a glance, Lawrence Butler’s first full year with the A’s has been merely okay. Butler delivered his first career walk-off on April 12, launching a 445-foot home run that same night, but through 30 games, he’s hitting .185 with a .599 OPS. Dig deeper, though, and Butler’s tantalizing potential becomes clear. He’s smashing the ball. He’s displaying more patience. He’s playing fantastic defense. He’s, in short, flashing glimpses of being a foundational piece. “I envision him being extremely successful,” Darren Bush, Oakland’s bench coach and director of hitting, said. “He’s big, strong and fast. When you have that combination and you’re willing to listen and you’re willing to learn and you’re willing to take information in and use it, you’re going to have a good chance of being successful.” The underlying number that immediately jumps out is his average exit velocity of 94.4 mph. Entering Friday, that places him in the 97th percentile, tying him with Shohei Ohtani and placing him just below Aaron Judge (94.6 mph) and Matt Olson (94.7 mph). It’s not just the exit velocity, either. Just about all