Most of the time, we can know from the stands when an on-side kick will be attempted. One team has just scored, is still behind, and needs the ball back. The rules state all players of the kicking team except the kicker (and holder if needed) shall be behind the restraining line at the time of the kick. The ball shall be kicked from some point on the kicking team's restraining line on or between the inbounds lines (Hash marks). For NCAA teams that line is the 30 yd/line unless relocated by penalty. The receiving team's restraining line is 10 yards beyond that line. Because teams tried to overload one side of the field for an on-side kick, a rule was introduced a few years ago that the kicking team must have at least 4 players on each side of the kicker. (The count includes the holder if one is needed.) Officials count the players, and won't allow the kick until both teams have the appropriate number of players on the field. The kicking team players must be inside the hash marks when the Umpire gives the kicker the ball, and the Referee blows the whistle for the ball to be ready for play, and the 25 second clock begins. At that time the players may move toward the sideline outside the hash marks.
The kicker may use a tee or may kick from the ground. In fact, the ball may be on the ground, resting in contact with the tee if the kicker so desires. The tee may not elevate the ball's lowest point more than 1 inch above the ground. If one reads the rules, a drop-kick is still legal for a kick-off, but is rarely used in today's game. (A punt may be used for a kick-off only after a safety, and usually from or behind the 20 yd/line unless relocated by penalty). If the ball falls off the tee, the whistle is sounded, the ball replaced, and the play clock restarted. A kicked ball after it falls off the tee, and the whistle blows, is deemed not to have been in play.
At the time of the kick, one official is stationed on each end of both the kicking and receiving team's restraining line, giving 4 sets of eyes on the happenings. First of all, the rule states a receiver must be given an unimpeded opportunity to catch the kick. That protection ends when the ball touches the ground, or is muffed by a member of the receiving team. So now the kicker kicks the ball into the ground directly off the tee, getting a short hop, and then a large, high hop. The officials must see that the ball has hit the ground to confirm the players do not now have protection to catch the ball.
Once the ball is kicked, the officials must rule whether everyone is behind the restraining line and a flag is thrown as a live ball foul if one is offside. The play continues. For a member of the kicking team to legally touch or recover the ball, the ball must have broken and remained across the plane of the receiving team's restraining line (10 yards), or have touched a receiving team member, or touched any player, ground, or official beyond the receiving team's restraining line. WOW! If a kicking team player touches the ball before any of the above occurs, a beanbag is dropped at the location of the illegal touching, and the play continues. When the play is over, the receiving team has the option of taking the ball at that point of illegal touching, if no fouls have been accepted. Illegal touching is a violation and does not offset a foul. Then a player being blocked by an opponent into the ball is NOT deemed to have touched the kick. This is another thing on which an official must quickly see and give a ruling.
Who ends up with the ball?
The pile builds rapidly and players are slow to get up. Under it all the players are fighting each other for possession. The official must dig into the pile to determine possession. Simultaneous possession is awarded to the receiving team.
If the ball takes too long and high of a bounce, and goes out of bounds untouched by a member of either team, then a flag is thrown for a kick out of bounds, and the choices are: (1) ask for a re-kick after a 5 yd penalty (doubt this will be a viable choice); (2) take the ball 30 yards from the point of the kick (usually the choice only if the kick is longer than 30 yards); or (3) take the ball after a 5 yard penalty from where the ball went out of bounds. On a short kick, that is often the best option.
Finally, a kicking team player may not block a receiving team player until the kicking team is eligible to touch the ball. The play in which 3 kicking players run into and block the receiving players backward so another kicking team member has an easy chance to recover is illegal; the kicking team blocked before it was eligible to touch the ball.
The next time you see an on-side kick, watch and see if you can spot all the above; did a foul occur; was there blocking too soon; did the ball go 10 yards; was the ball first touched by the kicking team before they were eligible to touch it; and would you have been accurate in your call? Oklahoma can tell you the officials at Oregon didn't exactly get it all right.