Black was searching for answers on Santana's eight walks and two wild pitches in 4 1/3 innings in a no-decision against the Royals, a game Kansas City won, 9-4.
So what was wrong with Santana?
"I don't know," Black said. "I haven't really seen that out of him. I think once you're out of whack, it is hard to get back into a rhythm. When you try too hard to get back into a rhythm, sometimes it goes the other way. I think that's what happened."
Black said he did not notice any mechanical defects from the dugout.
"I don't know if the heat affected him," Black said, referring to the 96-degree temperature at the first pitch. "I don't know if he was uncomfortable on the mound. He doesn't talk a whole lot during the course of the game. I'm going to talk to him today to see if he has any indications. I'm going to watch the video to see if I can pick up anything.
"I think once he got on a roll of throwing a lot of balls, he just couldn't get out of it. The harder he tried to throw strikes, the more he couldn't."
While there are concerns, the Angels are not overly worried about Santana, who is 7-0 in his past nine starts and 11-3 with a 4.20 ERA in 20 starts.
"It was just an aberration," Black said.
Bootcheck checks in: Right-hander Chris Bootcheck joined the Angels on Friday, recalled from Triple-A Salt Lake, where he was 4-2 with a 6.61 ERA in 28 games.
"Kevin Gregg has pitched three days in a row," Black said. "We felt we needed another arm just in case we had another game like we had last night."
Bootcheck was with the Angels earlier this season, getting into just one game before he strained his left hamstring on May 2 while running in from the bullpen during a team-wide altercation with the Athletics.
To make room for Bootcheck, the Angels optioned Tommy Murphy to Salt Lake. Murphy, a 26-year-old switch-hitting outfielder, hit .241 in 36 games. He hit .205 swinging left-handed and .316 right-handed.
"Murph needs to play," Angels manager Mike Scioscia said. "He's been sitting for a long time. Murph still needs to grow. His upside is big."
Erstad still out: Darin Erstad has missed 65 games this season with a right ankle irritation and there is no timetable when he might return. Surgery, however, has not been discussed.
"The word really hasn't come up," Scioscia said. "I don't know what they could do if there was surgery. I haven't heard any definitive thing they could do to fix it."
Note-ables: When DH Garret Anderson hit seventh on Thursday, it was his first time to bat seventh since May 3, 1999, against the White Sox. He hit fifth on Friday for the 10th time this season. ... The Angels, who committed an American League-high 77 errors entering Friday, have allowed 64 unearned runs, the most in the Majors.
Minor points: Left-hander Jonathan Rouwenhorst and three Salt Lake relievers combined on a 3-0 shutout of Fresno. Rouwenhorst allowed five hits, walked one and struck out four in five innings. He is 5-5 with a 4.32 ERA in 38 games, including two starts. Greg Jones worked the ninth and logged his 12th save. Second baseman Casey Smith doubled to extend his hitting streak to 10 games and is hitting .281.
Upcoming: Right-hander Kelvim Escobar (6-9, 3.88) and Royals right-hander Luke Hudson (2-3, 5.40) are the pitching probables on Saturday at 4:10 p.m. PT. Escobar has been on the disabled list with a right elbow irritation, but is scheduled to be activated Saturday.
Alan Eskew is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.