Rules of triathlon

Traditionally, triathlon is an individual sport: each athlete is competing against the course and the clock for the best time. As such, athletes are not allowed to receive assistance from anyone else inside or outside the race, with the exception of race-sanctioned aid volunteers who distribute food and water on the course. This also means that team tactics, such as drafting, a cycling tactic in which several riders cluster closely to reduce the air resistance of the group, are usually not allowed.
This has begun to change with the introduction of triathlon into the Olympics. Many Olympic-distance races, including the Olympics themselves and ITU World Cup events, now allow drafting during the cycling stage. This change has sparked extensive debate among the triathlon community, with supporters feeling that it brings triathlon rules closer in line with international cycling rules and practices, and opponents feeling that drafting has the potential to negate gains achieved by an individual in the swim, and gains an individual would have the potential to achieve during the cycling leg. Drafting has become the standard format for professional-level ITU events and the Olympics. However, the majority of amateur events retain the non-drafting format.
Triathlons are timed in five sections: 1) from the start of the swim to the beginning of the first transition (swim time); 2) from the beginning of the first transition to the end of the first transition (T1 time); 3) from the start of the cycling to the end of the cycling leg (cycling time); 4) from the beginning of the second transition to the end of the second transition (T2 time); 5) and finally from the start of the run to the end of the run, at which time the triathlon is completed. Results are usually posted on official websites and will show for each triathlete his/her swim time; cycle time (with transitions included); run time; and total time. Some races also post transition times separately.
Other rules of triathlon vary from race to race and generally involve descriptions of allowable equipment (such as wetsuits, which are allowed in the swimming stage of some races -- generally when the water temperature is below 79 degrees Fahrenheit or 26 °C), and prohibitions against interference between athletes.
One important rule involving the cycle leg is that the competitor must be wearing their bike helmet before the competitor mounts the bike and must remain on until the competitor has dismounted; the competitor may remove their helmet at any time as long as they are not on the bicycle (i.e. while repairing a mechanical problem). Failure to comply with this rule will result in disqualification.
Additionally, while on the bike course, a competitor is required to ride their bicycle at all times. Should a competitor's bike malfunction they can proceed with the race as long as they are doing so with their bicycle in tow.