NCAA Play

[Texas Aggie]

Had this last night, and when I got home, tried to put it together in the rules, but couldn't. It was late, and I was tired, so I might have glossed over something simple, but its at least worth discussing.

Fairly simple play: Pass thrown, intercepted and ran back for a TD by the defense. I'm R, and I flag a roughing the passer, but the roughing foul was pretty clearly AFTER the interception (pass was thrown right to a defender 8 yards or so away). What we did was give the ball to the intercepting team, mark 15 off from there, and go first and ten. It wiped out the TD, obviously. Note that the contact I flaged wasn't a block for an INT; the defensive kid had his eye on the QB the whole time and didn't know about the INT.

Right or wrong? What specific rules are in play? Would you change the call to an illegal block?