More than a month into the University of Wisconsin's 2005 football season, however, Casillas has become a special teams stalwart, starting on every unit except the punt team.
"In high school you (are) used to playing all the time," Casillas said. "You are a senior in high school you probably take off special teams because you play both ways or because you (are) playing so much.
"So it's kind of reminiscent of how it was my sophomore year in high school. Hey, when you (are) a younger player, you've got to be hungry. You've got to want it. And special teams is giving me the opportunity to hit people. And I haven't hit nobody since last year."
Casillas ended up missing just less than two weeks of fall training camp. And once he was ready to run the Badgers' coaching staff tossed him into the mix immediately, giving him plenty of reps with the scout defense at strong safety and on special teams.
"The first day I actually came to practice it was kind of surprising because they wanted to actually see me run," Casillas said. "Because I'd just been limping around and stuff like that. They kind of put me on scout kickoff, just to watch me on film run down the field a couple times.
"The next day I was on punt return and then like I did pretty good the first game against Bowling Green. I almost blocked a punt. So like the next game against Temple I was basically on like every special team.
"That shocked me now. I was like, everybody thought I was going to redshirt. I thought I was going to redshirt. My mom thought I was going to redshirt. I mean everybody thought I was, so it was a big surprise."
Another surprise occurred two weeks ago, when Casillas was moved from strong safety to the strongside "Sam" linebacker position. Casillas had been listed as a co-third team strong safety with fellow true freshman Aubrey Pleasant. He is now competing with sophomores Casey Hogan and Ben Landgraf for spots in the depth behind starter LaMarr Watkins.
"It's a big transition because I was getting really used to strong safety and backpedaling," Casillas said. "Now, it's more downhill now. I've got to make the transition… So I'm just learning and soaking up as much as I can from the older guys like LaMarr Watkins and Tez (Dontez Sanders) and (Mark) Zalewski. They've been real helpful, helping all the young guys out. Me, Casey Hogan and everybody. So it's been real good."
Casillas, who stands 6-foot, 203 pounds, was recruited as a strong safety or weakside linebacker. He was clocked at 10.4 seconds in the 100 meters in high school and has shown that athleticism off on special teams. Now, however, he must adjust to playing closer to the line of scrimmage, often jamming tight ends at the snap.
"When I got recruited they was talking about the Will and strong safety, like that's it," he said. "First time coach was like, ‘Yeah, I want to test you out at Sam,' I was like, ‘Oh, OK.'
"You know, it kind of caught me off guard a little bit. But I told coach I'm willing to do anything you want me to do to contribute. If that was to redshirt, if that was to play special teams, whatever."
Casillas said he hopes to weigh 220 pounds by next season.
"I've been running with the depth so far because basically because I'm not a redshirt," he said. "So I'm over there working out and I'm starting to get a little more into the action now because I've been watching, I've been listening, I've been going in to watch film a lot. So I'm kind of catching on.
"It's kind of harder to catch on at linebacker then it was strong safety, but I'm getting there."
Casillas was a quick study on special teams. He has two tackles this year and has come close to blocking several punts.
"It should be coming, man, soon," Casillas said of a blocked punt. "It should be coming soon."
Casillas' best feeling on a football field so far? Helping to contain Michigan kick returner Steve Breaston two weeks ago. Breaston was held to 47 yards on three kick returns during the Badgers' 23-20 win. Early in the fourth quarter, when Breaston hesitated on his way out of the end zone, Casillas, sophomore James Kamoku and true freshman Aubrey Pleasant combined to throttle him at the eight-yard line.
"He was supposed to be one of the big top kick returners and all that nonsense," Casillas said. "We flew downfield and I actually got a hit on him at the seven-yard line. And that kind of set the momentum for the defense and that fired everybody up. Me doing that as a freshman I was so souped up, I was so fired up. It's just a great feeling."