"Defensive pass interference is contact beyond the neutral zone by a Team B player whose intent to impede an eligible opponent is obvious and it could prevent the opponent the opportunity of receiving a catchable forward pass. When in question, a legal forward pass is catchable. Defensive pass interference occurs only after a legal forward pass is thrown. (A.R. 7-3-8:VII, VIII, XI and XII): It is not defensive pass interference (A.R. 7-3-8:III) (A.R. 7-3-9:III):
When, after the snap, opposing players immediately charge and establish contact with opponents at a point that is within one yard beyond the neutral zone.
When two or more eligible players are making a simultaneous and bona fide attempt to reach, catch or bat the pass. Eligible players of either team have equal rights to the ball. (A.R. 7-3-8:IX)
When a Team B player legally contacts an opponent before the pass is thrown. (A.R. 7-3-8:III and X)
When there is contact by a Team B player that otherwise would be pass interference during a down in which a Team A potential kicker, from scrimmage kick formation, simulates a scrimmage kick by throwing the ball high and deep."
There doesn't appear to be an exception to the pass interference rule for a tipped ball. I'm pretty sure when the refs signal that the ball is tipped, it's to indicate that a tip or deflection rendered the pass uncatchable. If the pass is tipped but still catchable, the rule suggests that interference may still be called.
Defensive holding is when the defense impedes any eligible receiver, whether the ball is being thrown his way or not. It automatically becomes pass interference the moment the pass crosses the LOS and is catchable by an eligible receiver.
