The need to get bigger has been well chronicled (and first heralded by Bud Elliot) here at TN. Do yourself a favor and read the "Size Matters" articles pinnned along the side of the website and make liberal use of the "Search" function. Then take a look at the following:
FSU’s projected starting safeties:
Nick Moody – 6’2" – 228 lbs.
Terrance Parks – 6’2" – 218 lbs.
vs. 2009 starting backfield:
Mangum – 6’0" 200 lbs.
J. Robinson – 6’2" 188 lbs.
vs. projected starting backfields from around the league:
Brandon Taylor | 6-0, 191, So., 1V
Jai Eugene | 5-11, 182, Jr., 2V
Marty Bowman | 6-2, 217, Jr., 3V
Wes Davis | 6-1, 221, GS1., 2V
Ahmad Black | 5-9, 190, Sr., 2V
Will Hill | 6-1, 207, Jr., 2V
Joseph Nicolas | 6-1, 205, Jr., 3V
Vaughn Telemaque | 6-2, 207, So., 2V
That's an astounding 60 lbs. difference in safety size from 2009 to 2010 for FSU, and anecdotally heavier than many other major CFB safety groups. This reflects a fundamental difference in personnel philosophy at the safety position. Moody did see action last year, but not enough, especially when considering who was above him on the depth chart ^shudder^.
Look for Stoops to demonstrate the same base coverages he employed against heavy-spread offenses such as Oregon: Cover 3, and Cover 4.
Arizona is in a 4-3 alignment here, but both safeties are within 10-12 yards of the LOS scrimmage. This is classic quarters coverage: 2 CBs and 2 S have deep zone coverages, with each player responsible for "1/4" of the deep field. With so many bodies guarding deep, the safeties can creep up to potentially help in run support.
Later in the game, same alignment, same philosophy regarding safety depth: They are available to help underneath. And to hit.
UA commits more guys to the box here to give a 4-4 look; most likely the SS has walked up into the box. This is what a 4-3 Cover 3 eventually looks like as a play develops. UA has just chosen to give this look pre-snap.
All of this is just to say that the safeties will be active in the run game, and they'll be bringing 60 more pounds with them this year.