This is in the Ohio 2009 Season Manual for coaches and officials.
Sideline Safety
The sideline SHALL be clear of all players and coaches from the sideline to six feet outside the sideline. Please review NEW rules 2-3-g and 10-8-3. As a practical application – when the center touches the ball, the restricted area will be clear.
B. There is no longer a “coaches box”. When the ball is live no one shall be within 6 feet of the sideline. When the snapper touches the ball the restricted area will be cleared. All players and coaches shall be in the team box.
http://www.ohsaa.org/sports/ft/boys/manual.pdf