"I'm still working on that part," Santiago said, laughing. "You never know if it's going to break 24 inches or if it's going to break eight inches."
The pitch is a screwball, which can either be defined as a changeup with more depth or a curveball that breaks in the opposite direction -- and is hardly thrown because it's so difficult to properly execute.
Christy Mathewson was throwing some semblance of it at the turn of the century, Carl Hubbell revolutionized it in the 1930s, Tug McGraw went to it often during two All-Star seasons in the 1970s, and Fernando Valenzuela spotted it brilliantly to his catcher, Mike Scioscia, in the 1980s.
Santiago adopted it because he had nothing to lose.
It was the winter of 2010. Santiago, on the verge of turning 23 and once again playing winter ball in Puerto Rico, had just completed his fourth season of pro ball, had yet to advance to Double-A and the White Sox were trying to salvage his career by turning him into a submariner. Santiago thought back to two winters ago, when former Brewers lefty Angel Miranda told him he had the perfect arm slot for a screwball and taught him the pitch, and figured this was as good a time as any to break it out in games.
"I'm not a top prospect, I'm a 30th-rounder. They have no money invested in me," Santiago recalled. "I'm like, 'Why not?'"
Santiago grew up in New Jersey, where high school baseball isn't very competitive and someone who throws 90 mph can survive on fastballs alone. Santiago didn't throw an offspeed pitch until he was 22 and had no idea what a screwball was until he felt it come out of his hand.
It was so impressive by the winter of 2010 that his coach sent a three-page, handwritten letter to White Sox management, urging them to let him throw the pitch. And by the time he showed up to Spring Training, Ozzie Guillen actually knew who he was.
"Aren't you that guy with the Bugs Bunny pitch?" the gregarious skipper told Santiago. "All right, we're going to see it."
Santiago showed it off in spring, went from Class A Advanced to Double-A to the Majors in a little more than three months, and became an integral starter and reliever for the White Sox over the next two years, posting a 3.33 ERA in 70 1/3 innings in 2012 and a 3.56 ERA in 149 innings in '13.
John Hester was the first Angel to catch Santiago's screwball when he arrived at Spring Training, two months after being acquired alongside Tyler Skaggs in the three-team deal that sent Mark Trumbo to the D-backs.
"I've never seen anything like it," Hester said. "It's just a super-slow changeup that goes the wrong way."
Jered Weaver was standing next to Santiago when the lefty all of a sudden shouted "screwball" at Hester, and the Angels' ace was stunned. Albert Pujols remembers how badly he got jammed by the 60-mph screwball of former Reds reliever Danny Herrera and saw some of Santiago's during live batting practice last week.
"It's pretty good," Pujols said. "But I told him not to throw too much because you don't want hitters getting used to it."
Santiago remembers looking at the left hand of Luis Arroyo, an All-Star with the Yankees in 1961, and noticing how his last three fingers naturally tilted to the left because he threw so many of those screwballs. Santiago has never had any arm problems, but if he extends his arms, his left one has a natural bow to it from throwing that pitch.
The Angels say they aren't concerned about the health risks that come with the screwball, though.
"It's actually medically checked out just fine," general manager Jerry Dipoto said.
"When you throw a baseball, your arm pronates anyway, so you're pronating it a little more, from what I understand," manager Mike Scioscia added. "Any pitch, like a slider, if you do it correctly, it's no threat to your arm."
But Santiago will go out of his way to tell you he isn't defined by the screwball. It's actually ranked fifth in his repertoire depth chart, behind the low- to mid-90's fastball and the changeup, cutter and slider. He didn't throw it more than a handful of times per game during his last two years with the White Sox.
But that may change this season.
"I want to mix it in more now," Santiago said. "It's definitely a pitch that can throw people off, and it's been great for me. Hopefully this is the year that I bring it in a lot more. I think I'm ready for that."
Santiago always defers to his catchers, and Chris Iannetta called for four of them during Santiago's 2 2/3-inning outing against the A's on Sunday. One resulted in a weak grounder, and the other three went for strikes.
"Depending on how consistent he can be with it, he's going to just use it like a changeup -- another offspeed pitch," Iannetta said. "Just use it to get guys off-balance."
At some point this spring, the Angels hope to get Santiago and Valenzuela, now a Spanish broadcaster with the Dodgers, to sit down and talk about the screwball. And as the 26-year-old left-hander continues to pile up innings in Cactus League play, he hopes to grow more comfortable with it.
"If it's working like it was today," Santiago said, "I don't mind throwing it a lot."