Judo and Rei - Etiquette
The spirit and protocols of Rei are one of the fundamental aspects when learning Judo (i.e. Seiryoku-Zenyo and Jita-Kyoei) in the dojo. At the same time, Rei also becomes indispensable in one's daily life.
As described in the "Judo Competition Etiquette" rules that were enacted in 1967:
Upon the first meeting of the contestants, the match will begin with a Rei (bow) as a demonstration that each recognises the character of the other person, and is showing respect towards them. More than just a way for people to associate with each other, the spirit of Rei serves as a system to preserve social order, and Reiho (etiquette) are the protocols that represent it. Practitioners who learn Seiryoku-Zenyo and Jita-Kyoei deepen their appreciation of this spirit of Rei, but it is important that they outwardly display proper etiquette as a manifestation of this.
In the Kodokan, the spirit of Rei is afforded great significance, and we emphasise the importance of etiquette as a representation of this spirit. In Judo practice or competition, the protagonists look to defeat each other as they grapple. If the spirit of Rei is lost, the encounter descends into a violent struggle, a fight, and the possibility to learn anything of any value falls by the wayside. It is easy to become excited and resort to unscrupulous behaviour when obsessed with victory or defeat. However, Judo bouts provide an important opportunity for forging one's mind and body through keeping calm and reflecting on the spirit of Rei to maintain self-control.
Etiquette, otherwise known as Reiho, is the physical manifestation of the spirit of Rei. Zarei (seated bow) and Ritsurei (standing bow) are usually taught in the dojo. These two types of Reiho are the focus of instruction, but they are not everything. As Reiho is the method of expressing the spirit of Rei, it is important to understand that this spirit must not be lacking, notwithstanding of the situation, time, or way it is expressed. When interacting with others, one judges the situation and acts in a specific way. You must ask yourself whether you are truly representing the Judo ideal and the spirit of Rei. The point being, there is a difference between merely complying with the forms of Reiho, and performing it the true spirit that underlies it.
After every bow, reflect on the spirit with which it was executed. Let us strive to do correct and polite Rei, brimming with sincerity. With the first Rei in a Judo practice, you and your opponent join as partners, and the greeting expressed means, "Let's start to refine ourselves together through this training". The Rei at the end of practice is an expression of gratitude: "Thank you for being my partner." Rei performed in the dojo, it can be said, should be observed at all times in order to enact the spirit of Jita-Kyoei in one's everyday life.
Reference: Shinichi OIMATSU, "Japanese Budo: Judo"