OPI restrictions begin at the snap, all DPI restrictions begin only once the ball is in the air.
PI can only be called on a catchable pass that crosses the neutral zone untouched. The contact must be beyond the neutral zone. For DPI, the ball must be thrown to the receiver in question (not true for OPI).
There is no illegal contact rule in college like there is in the NFL. In college a DB can block a receiver for as long as the receiver could theoretically block him, i.e., as long as the receiver hasn't reached the same yard line as the DB.
PI can only be called on a catchable pass that crosses the neutral zone untouched. The contact must be beyond the neutral zone. For DPI, the ball must be thrown to the receiver in question (not true for OPI).
There is no illegal contact rule in college like there is in the NFL. In college a DB can block a receiver for as long as the receiver could theoretically block him, i.e., as long as the receiver hasn't reached the same yard line as the DB.