Don’t forget the fact that it would be impossible to tell were certain injuries are actually caused by turf:

Ankles break because someone drops on your leg.

Concussions can happen on head-to-head contact.

Players can run into goal posts, walls, benches, etc.

If a player comes into a game with a nagging/minor injury from a grass field that is exacerbated on a turf field, how should that be counted?

If a player is injured on a grass field and tells no one but plays at 70% of his total ability the remainder of the season, how should that be counted?

Does offseason conditioning impact on-field injuries more than playing surface?

The above “injury” questions are difficult to answer definitively because of different pain tolerances among individuals, acute (broken bone) vs. ongoing (tendonitis) nature of various injuries, etc.

All of the injury-related questions fall outside the author’s premise — namely, that of assessing numerical, statistical performance as it relates to playing surface.

I addressed this yesterday, injuries are not a stat. Here’s why: http://www.herloyalsons.com/blog/2014/02/11/notre-dame-field-turf-offense-checking-the-narrative/#comment-256497

The stats are compiled over the entire BK era, not just last year.