There are only a few penalties that are automatic first downs. Roughing the passer, roughing the snapper (on punts and field goal tries), roughing the kicker, and roughing the holder are the only penalties (if I am wrong tidehawk please correct me) that are automatic first downs. Just because the penalty is 10 or 15 yards against the defense doesn't make it an automatic first down. It depends on where the penalty is enforced and if the yardage gained makes it a first down. During my game Friday night, we had a good many penalties that were 15 yards and you could here the crowd (and coaches) screaming that it should be an automatic first down. In college that may be the case, but in high school it is not.