Late to the field??

[BoBo]

What is the penalty for being late to the field under NFHS rules. For example: Halftime is 15:00 minutes clock reaches 0:00 and team not on field. Obviuosly we still have 3:00 minute warmup but team has was not on the field before 0:00.
We had last night and were not sure between delay of game and unsportsmanlike. We went with unsportsmanlike 15 yards on the second half kickoff. I guess you could have a similar situation before the game as well.
Any comments??