Penn State coach Bill O'Brien knew depth was going to be an issue for his team before the season started, and the first three weeks have severely tested that depth.

Bill O'Brien is hoping to get some of his injured players back this week.
He has a chance to rebuild it a bit this week.
The Nittany Lions will hold walk-on tryouts on Wednesday after practice, and the head coach is hopeful they might be able to add a player or two to the secondary, easily the thinnest unit on the team.
"I would say positionally, maybe there are a couple DBs in the crowd there," O'Brien said during Tuesday's news conference in Beaver Stadium. "You know, that's usually the position right now that we're looking for because of numbers‑wise.
"Other than that, I just want to try to get out there and see if we can find some good football players," O'Brien added. "You know, guys that are just hungry to play football that can move around a little bit, maybe catch the ball well. Maybe they're bigger guys that we think have a future as a lineman."
O'Brien did not mention placekicking when talking about the tryouts. Penn State will continue to go with Sam Ficken, who is 1-of-5 on field goals and 7-of-9 on extra point this season. He said that Ficken had gone 10-for-10 on field goals in practice the previous week but admitted that he "needs to continue to get better at his technique."
Depth at defensive back and kicker remain long-term issues, but Penn State's depth at two other positions -- running back and offensive tackle -- has caused some short-term troubles. O'Brien said Tuesday that Derek Day was slightly further ahead in his recovery from a shoulder injury suffered against Virginia than Bill Belton was in his recovery from his ankle injury suffered against Ohio but that both were still "day-to-day."
"These guys get beat up during the season," O'Brien said. "They're running backs; that's the nature of the position, so the next guy has got to be ready to go. We've gotten decent production out of other guys. Curtis Dukes came in and did some good things on Saturday; (Michael) Zordich did some good things; (Zach) Zwinak needs to probably play a little bit more. So we've got some guys there that can step up, we believe."
Left tackle Donovan Smith, who also missed the Navy game, remains a question mark this week with a right ankle injury.
"Donovan is day to day," O'Brien said. "I know you guys hate that answer, but it's the truth. If he comes out today and he can move around, then maybe he's got a better chance to play. If he comes out today and he's gimpy, then probably won't play."