Question on NCAA Enforcement

[kd0254]

Watching an NCAA game and I have a question on enforcement that if done correctly was different then I would have thought.

2nd and 10 for Team A on the B 20 yard line. A12 drops back to pass and throws a completed pass to A88 at the B15 yard line. A88 is hit by B22 and fumbles the ball at the B15 yard line. The ball lies motionless for a second and B28 comes in and clearly bats the ball backwards to the B25 yard line where A77 recovers. There is a flag thrown at the 15 yard line for an illegal bat by B28. In the game (2009 game I think) the penalty was enforced half the distance to the goal from the previous spot making it 1st and 10 at the 10.

From my thoughts I couldn't understand how previous spot would come into play, but I deal more with NHFS then NCAA. I would have thought this would be enforced from the 15 yard line as the end of the related run (I am sure I would enforce from there in NFHS).

Thoughts? Rule references?

Thanks.