Lightsaber Duel Challenge
In FFA players can challenge each other to a duel by looking at a player and using the engage_duel command (Default key: k). To accept, the challenged player looks at the challenger and uses the command. They will then become transparent to other players and will become unable to interact with other players. The duel ends when either player dies or they move too far apart, severing the duel. In base jka only one duel can occur at a time.
Japlus Changes
Japlus, (and other mods) change a number of things about duels. Duel effects are changed, making players outside of the duel completely invisible to the duellists, duel-severing is disabled and HP is resent to default before and after the duel.