[CecilOne]

Here is a summary of the triple system of officiating (usually called double-dual or three-whistle) which I wrote for officials in our association who would be using it. Most of them preferred it.

The purpose is better coverage, seeing accurately what happens on every part of the field. The advantages are having a trail official closer to play, more flexible positioning for how the specific part of the game is being played and better match control because of increased presence. The triple system covers the middle of the field better than the dual system and covers the ends of the field better than the single or diagonal system, particularly the interior penalty area.

All three officials are equal and share responsibilities and authorities equally, except for the head referee responsibilities in Rule 5. The head referee designation (by assigner or crew choice) has nothing to do with the positions on the field. All work and communicate together as a team. Proper signals, especially prompt "play on", and observing each other are required so calls do not overlap.

Dynamic play:
All three move on or off the field based on the needs of the moment to stay close to the players.

The end referees (ER) work much like the dual system, except for not covering as much of the opposite end of the field as trail. They box in all the players, make all the calls and decisions for play nearest them and usually make most of the calls. The ER’s give priority to the “horizontal” line of sight.

The middle referee (MR) works as a “permanent” trail (vs. lead), boxing in the active play with the current lead, managing free kicks and kickoffs, balancing the positioning and angles of the crew, positioned for “trail” fouls, etc. The MR can penetrate deeper in each end and closer to the lead ER side than a dual system trail. The MR gives priority to the “vertical” line of sight.


Kickoffs
ER ready for attacks and offsides (NL defender)
MR near mid-line (kicker, encroachment)

Throw Ins
ER if nearest side, MR near expected action
MR if nearest side, ER near expected action or offsides

Goal Kicks
Lead ER positioned for attack and offsides
MR near expected action point
Trail ER near goal area, sound whistle if needed

Corner Kick
Lead ER outside goal line near goal area line
MR near trail side of penalty area
Trail ER near mid-field or NL defender

Free Kick
Lead ER ahead of ball, positioned for attack, offsides or goal
MR in line with ball, positioned for encroachment, manages “wall”
Trail ER behind ball positioned for counter attack

Free Kick near goal and Penalty Kick
Lead ER near goal line (goal judge)
MR positioned for offsides, encroachment, manages “wall”
Trail ER behind ball half way to mid-field, positioned for “trail” fouls

The referee on the home bench side is the primary timer.