There is no such offence as "high boot". However, if a player swings their boot near an opponent's head without contact occurring, there are two offences that may have been committed.
If contact has occurred, it's just a regular carelessly / recklessly / excessively forcefully kicks an opponent offence, which results in a direct free-kick or penalty kick like most other fouls.
The tl;dr is -
- If the opponent is forced to not play the ball to avoid potential injury, an indirect free kick is awarded for playing in a dangerous manner.
- If the swinging foot is a near-miss, even if the opponent has not pulled out of the challenge, a direct free kick may be awarded. Depending on the severity of the challenge, a caution or send-off may be issued.
- If either of the above offences occurs and:
- a promising attack is broken up, the player committing the offence is cautioned for unsporting behaviour; or
- an obvious goalscoring opportunity is denied, the player committing the offence is sent off.
The first offence is playing in a dangerous manner. Law 12.2 states:
An indirect free kick is awarded if a player:
- plays in a dangerous manner
Playing in a dangerous manner is any action that, while trying to play the ball, threatens injury to someone (including the player themself) and includes preventing a nearby opponent from playing the ball for fear of injury.
A scissors or bicycle kick is permissible provided that it is not dangerous to an opponent.
As seen there are two elements to this offence, the first is:
- a player does something that places either themselves, a teammate, or an opponent at risk injury
- a nearby opponent avoids playing the ball in order to avoid injuring whoever it is that has been put at risk of injury.
Here are some examples of what would constitute playing in a dangerous manner:
- A red player attempts to kick a ball at head height, close to the face of a blue player. The blue player avoids playing the ball to avoid being kicked in the face.
- A red player falls on the ground, landing on top of the ball. The red player continues to lay on the ball, making no real effort to get up. A blue player avoids kicking at the ball so that they do not kick the red player.
- A red player dives head first at a shin height ball to play it. A blue player, who otherwise would have been able to clear the ball, avoids kicking the ball so that they do not kick the red defender in the face.
In all of the above examples, the red player has committed the offence of playing in a dangerous manner.
As counterexamples, here are two incidents that are not playing in a dangerous manner, but are often incorrectly called as such:
- A red player kicks at a ball at head height near a blue player's face. There is no contact, and the blue player manages to get a head to it first. The blue player then loses control of the ball and begins appealing for a "high boot". There is no offence, as the blue player was not prevented from playing the ball.
- A red player falls on the ground, and begins flailing at a nearby ball whilst lying on their back. A blue player rushes in and attempts to play at the ball, before the red player manages to kick it away. There is no offence, as the blue player was not prevented from playing the ball.
If the referee believes a player has committed the offence of playing in a dangerous manner, the restart is an indirect free kick to the opponents.
Note: if contact occurs, the foul must not be sanctioned as playing in a dangerous manner, and a direct free kick offence should be considered instead.
The second offence is carelessly, recklessly, or excessive forcefully tackling or challenging an opponent. Law 12.1:
A direct free kick is awarded if a player commits any of the following offences against an opponent in a manner considered by the referee to be careless, reckless or using excessive force:
In 2016/17, the word "challenges" was added to this offence, to indicate that referees should not just be looking at "tackles", but all contests for the ball. Given the definitions of careless, reckless and excessive force, it seems plausible that swinging a foot within centimetres of an opponent's head as they're trying to play the ball, resulting in a near-miss, could be considered careless at the very least.
The other advantage of taking this approach, is that the referee does not need to wait and see if the opponent is prevented from playing the ball by the challenge. As soon as the challenge occurs, as long as it is careless, reckless, or excessively forceful the direct free kick may be awarded.
As described in this answer, if the challenge is careless, just the direct free kick is awarded; if reckless, the player concerned is also cautioned for unsporting behaviour. Finally, if there is excessive force, the player concerned is sent-off for serious foul play (assuming it was a challenge for the ball).
No matter which solution the referee uses to deal with players swinging boots near an opponent's head, the tactical nature of the offence (as with any offence) should be considered.
If the offence breaks up a promising attack, the player is cautioned for unsporting behaviour.
If the offence results in an obvious goalscoring opportunity being denied, the player is sent-off.
There are different circumstances when a player must be cautioned for unsporting behaviour including if a player:
- commits a foul or handles the ball to interfere with or stop a promising attack
A player, substitute or substituted player who commits any of the following offences is sent off:
- denying an obvious goal-scoring opportunity to an opponent moving towards the opponents’ goal by an offence punishable by a free kick (unless as outlined below)