Coaches and Runners
The role of the coach in Aussie Rules is different compared to other sports in that the coach is only able to address his players before the game, and then during the quarter-time, half-time and three-quarter-time intervals. There are no time-outs in Australian Rules. The coach usually sits in a box above the ground with his assistants, analyzing the game in progress. When a change in tactics or players is desired, the coach sends his orders (usually by picking up the field telephone) to the club's runner.
The runner is allowed on the ground during play to communicate to players and relay the coaches' instructions. You'll notice him because he's wearing the neon warm ups.). Runners often spend so much time on the ground that they assume the duties (if not the title) of assistant coaches, helping with team decision making. When on the ground during play, the runner must attempt to stay away from the football and out of play. The coach will also address the team at the quarter-time and three-quarter-time huddles, and when the team comes off the ground at half-time.
The AFL has cracked down on runners who spend an undue amount of time on the ground and appear to be "coaching". Runners deemed to have interfered with the progress of the game in such a manner, or touch or interfere with opposition players can be fined or suspended by the league.
Trainers
A team can nominate 5 trainers that are allowed on to the playing field to assist with injured players, or provide help (e.g. fluids) to players. Except in the case of an injury, the trainers are only allowed on the ground when there is a pause in the play (e.g. between a goal being scored and the restart of play.)