Five things we learned in the spring, No. 3

USC’s spring practice is done and football is officially over until the first week of August, so we’re going over the five biggest things we learned this spring.

We went over De’Von Flournoy‘s surprise spring Monday and defensive back depth on Tuesday. Our third -- and first not-so-great -- thing we learned over this year's spring practice is this: Both USC tackles still have a lot of work to do to learn how to best defend speed ends.

Lane Kiffin mentioned it more than once over the course of the Trojans' 15 spring practices.

He was generally happy with the progress of the team's interior offensive line throughout the spring. Center Khaled Holmes wasn't always healthy, but, when he was, he was demonstrating improvement. Right guard John Martinez was quietly good. And sophomore left guard Marcus Martin proved nimbler on his feet after an offseason in the conditioning program.

But the offensive tackles, blind-sider Aundrey Walker and right tackle Kevin Graf, left a little something to be desired -- specifically, both players demonstrated a number of times they're not yet well-equipped to defend speed-rushing defensive ends. Devon Kennard and Wes Horton got by them on the outside with ease.

"That's been an issue for us," Kiffin said last week, after USC's spring-concluding Spring Game.

And that's slightly alarming, because the Pac-12 has a ton of ends who are even more pass-rush-oriented than Kennard and Horton. So is it a full-on structural thing, where Walker and Graf just aren't capable of turning their hips quick enough to prevent ends from getting the edge? Or is it just a time thing, where they both need time to develop better technique?

For Walker, at least, there's hope that it's the latter. He lost more than 50 pounds since last season, down to 320, and his footwork has already dramatically improved over the past few months. There's no reason to think he can't continue to get better and grow more comfortable with it.

And, for Graf, he actually proved last year to be reasonably adept at pass-blocking, save for the Arizona State game, which was downright disastrous for him. He's not an incredibly heavy guy -- he has to work to keep his weight up near 300 pounds -- so there's also reason to believe he'll be able to handle the 230 or 240-pound types come September and October.

So what's to make of all this talk? We'll get a better sense in the first couple weeks of fall camp, especially when USC brings in top-prospect Leonard Williams and he gets to work on Walker as a right end.

For now, it's an area of minor -- but legitimate -- concern.

Check back Thursday for the fourth thing we learned in the spring, involving grand-scheme changes the Trojans are slowly but surely making to their defensive unit.