Sports are very unpredictable.

Just ask a Vegas bookie about USC’s home loss to Stanford in 2007.

Or about the likelihood of Notre Dame’s fourth quarter near-comeback against the Trojans three weeks ago.

Or even about the chance that a home underdog would beat the then-No. 5 team in the nation by 27 points.

But if there is anything certain about sports, it’s that a team will suffer injuries.

Every team does, and a big part of what determines a given team’s success is the collective reaction to injuries over the course of a season.

But at the end of that season, frequently the biggest indicator of relative success is how many of a team’s expected starters finish the season in a starting role.

And no matter how many times coaches tell you that you can have rookies, freshmen and inexperienced players take over for your veteran expected starters, nothing compares to having as many starters as possible actually start.

The more, the better. The fewer, the worse.

Just take a look at this year’s Trojans.

Let’s estimate how many collective games have been missed by starters or significant contributors for USC this season and try to evaluate the job done by the fill-ins.

At quarterback, true freshman starter Matt Barkley sat out the Washington game with a bruised throwing shoulder. Redshirt sophomore Aaron Corp made his debut as a starter and was widely blamed for the 16-13 loss.

Senior running back Stafon Johnson has missed four games since suffering a tragic weightlifting injury to his throat and is out for the remainder of the season, although redshirt junior Allen Bradford has performed admirably in his absence.

Redshirt junior fullback Stanley Havili has been out for the last two games with a dislocated right shoulder. Sophomore D.J. Shoemate has stepped in and blocked well, but hasn’t caught a pass.

At receiver, juniors Ronald Johnson and David Ausberry have missed a combined eight games. Redshirt freshman Brice Butler has grown into a fourth receiver role, but a lack of targets has admittedly hurt the Trojans’ offense thus far.

Senior tight end Anthony McCoy missed the Oregon game with a sprained ankle. McCoy had caught seven passes for 178 yards and two touchdowns in the last two games, but his replacement, sophomore Rhett Ellison, didn’t catch a single ball.

The offensive line has been the least affected, but still, junior center Kristofer O’Dowd — USC’s offensive lineman of the year in 2008 — sat out the season opener and the last two games, as he is recovering from a dislocated kneecap.

On the defensive line, projected starter Armond Armstead was out for the first five games and is now hurt again with a broken wrist. At the opposite end, junior Everson Griffen, was hobbling this week in practice with turf toe. For the most part, young defensive ends Nick Perry and Malik Jackson have played well, but the defensive line completely collapsed against Oregon.

Junior weakside linebacker Malcolm Smith has missed two games and is likely to miss more with a shoulder injury. One of the backups who could replace him, redshirt sophomore Jordan Campbell, missed four contests but could return this week.

Besides expected starter redshirt junior Shareece Wright’s academic ineligibility switching around the defensive backfield, the Trojans have also had to deal with senior safety Taylor Mays missing a game, junior safety Drew McAllister missing two, and serious injuries to nickel and dime contributors junior Marshall Jones and redshirt freshman Brian Baucham — totaling nine missed games.

Count them all up, and that’s 42 man-games missed by key contributors out of a total of eight games this season.

Compare it to UCLA’s 11 defensive starters missing a combined one game.

The traditional coach-speak book says in these situations that other, less-experienced players will step up to fill the veterans’ void.

“We have a great history here of guys stepping up and playing really well and coming through,” USC coach Pete Carroll said in his Tuesday press conference. “That’s the only way we know how to expect that to happen. And that’s what we’re counting on. Nobody’s come here to just sit around.”

And few will be able to.

There exists a certain point where injuries ravaging a team become more than just setbacks. At some point, they become part of a team’s collective psyche.

How do you know when? It happened against Oregon.

USC did not play with its traditional fire. You saw guys shy away from hits routinely. Oregon weapons quarterback Jeremiah Masoli and running back LaMichael James literally ran over the Trojans on multiple occasions.

It’s the point where mental meets physical and physical meets mental.

“It’s not just the mental things, it is the physical side and getting them ready well so we can play,” Carroll said. “We’re doing it, and I think these guys are pretty resilient.”

Only the coming weeks will tell.

“Looking Past the X’s & O’s” runs Wednesdays. To comment on this article, visit dailytrojan.com or email Pedro at pmoura@usc.edu.