The 2011-20112 Rule reference is Rule 10-1-4:
Offsetting Fouls
ARTICLE 4. If live-ball fouls by both teams are reported to the referee, the fouls offset and the down is repeated (A.R. 10-1-4-I and VIII).
Exceptions:
1. When there is a change of team possession during a down, and the team last gaining possession had not fouled before last gaining possession, it may refuse offsetting fouls and thereby retain possession after completion of the penalty for its foul (A.R. 10-1-4-I-VIII).
2. When Team B’s foul is governed by postscrimmage kick rules, Team B may refuse offsetting fouls and accept postscrimmage kick enforcement.
3. Rules 8-3-4-c and 3-1-3-g-3 (during a try or extra period after Team B possession).