Game concept
Likelihood of Success
The game also links it as Duel Success.
From the game's encyclopedia
When fighting a Single Combat, your Likelihood of Success is how well you are doing in the Duel. To win, you must get your Likelihood of Success far above your opponent's.
As rounds go on, it becomes easier to win, meaning you need less lead over your opponent.
The counterpart to Likelihood of Success is Risk of Injury.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Likelihood of Success is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "When fighting a Single Combat, your Likelihood of Success is how well you are doing in the Duel." It is part of Single Combat. The game also links it as Duel Success. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.