NCAA/NBA RA in layman's terms
 

Trying to explain the RA to my father who has a slightly higher basketball understanding than most fans in the stands.

Any ideas especially since I have little understanding of NCAA rules/mechanics.

NBA:

The RA is an area on the court which doesn't allow secondary (help) defenders attempt to take a charge. If a player is located in this area for the purposes of taking a charge, it's an automatic block.

Now there are situations where an offensive foul can still be called...if an offensive player leads with a foot or elbow for example. Also if a play originates close enough to the basket (known as the lower defensive box) then the RA doesn't apply. And the RA also doesn't apply if a defender jumps in an attempt to block a shot.

NCAA:

A secondary (help) defensive player can't take a charge in this area unless it is an unnatural movement (leading with a knee or arm, for example) or a "stop-start" move.