In his first 21 appearances before landing on the disabled list with right elbow soreness last season, Casilla posted a 0.93 ERA and an opponents' batting average of .185. In his 30 appearances after coming off the DL, his ERA was 5.81 with an OBA of .353.
In his first nine appearances before landing on the DL with a sprained right knee, Casilla posted a 1.59 ERA. In his nine appearances since returning, his ERA is 12.38.
OK, maybe Thome's 550th homer, which played a huge hand in dealing the A's a 6-2 loss in the opener of a four-game series at U.S. Cellular Field on Monday, wasn't in the air that long.
But it was up there plenty long enough to make you wonder why Casilla has been alternately one of Oakland's most reliable and most combustible relievers over the past few seasons.
"He's given up some runs here since he came back, but he's had his stuff, and his [velocity] is there," said A's pitching coach Curt Young. "But when you come in as a reliever, you're not going to be throwing man pitches, so when you make two or three mistakes, it's really going to hurt you.
"And Santiago, it seems like he's had a couple location mistakes every time out here lately."
The 1-2 breaking ball Casilla threw to Thome was supposed to bounce in the dirt. Instead, it hung out over the plate, a virtual "crush me" sign affixed.
"You do that with any hitter, it's probably going to get hit hard," A's manager Bob Geren said in the narrow hallway outside his office after the game. "Do it with a guy like Thome, it's probably going to go a long way. And it did."
In eight innings since being activated, Casilla has given up 11 earned runs on 16 hits -- four homers -- and six walks.
"I don't think that there's an issue with his leg. Health-wise, I think he's fine," Young said. "It's just a matter of putting the ball where he needs to put it."
Casilla isn't the only reliever making mistakes. The bullpen as a whole has allowed 27 runs in 29 innings over the past 10 games (8.38 ERA), and a unit that posted a 2.62 ERA in April has checked in at 5.52 since that page on the calendar turned.
"All of our guys are kind of hitting the skids," Geren said. "A lot of them were pitching so well at the same time early in the year, and now a few of them are struggling at the same time."
A's starter Trevor Cahill didn't struggle very often Monday, but as is often the case, the Oakland offense struggled to support the 21-year-old rookie.
Cahill held the White Sox to three hits while walking two and striking out three over 5 2/3 innings, but the second of the three hits was a game-tying solo homer by A.J. Pierzynski in the fifth. Floyd held Oakland to two runs on four hits and three walks over seven innings.
"He's good," Pierzynski said of Cahill, who has gotten zero, one or two runs of support in seven of his 11 starts this season. "He has a lot of movement on the ball. His ball really sinks and moves, and he changes speeds on it very well. It makes it tough, as a hitter, to square him up."
Matt Holliday, batting .358 (24-for-67) over his past 20 games, squared up Floyd in a big way in the top of the first inning, following a two-out single by Jack Cust with his seventh homer of the season, a mammoth shot deep into the left-field bleachers.
In the bottom of the frame, Holliday stole a two-out home run from Paul Konerko with a leaping catch at the left-field wall, but not before the White Sox cut the lead in half. Scott Podsednik drew a leadoff walk, moved to third on a hit-and-run single by Alexei Ramirez and scored on a sacrifice fly by Jermaine Dye.
Lefty Craig Breslow pitched well for Oakland after Cahill left, providing 1 1/3 innings of shutout work before he walked the leadoff man in the eighth. Casilla took over, gave up a one-out single to Dye ahead of Thome's blast, then walked Konerko to earn his exit.
Mychael Urban is a national writer for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.