Performance accomplishments are the strongest contributor to sport confidence. When you perform any skill successfully, you will generate confidence and be willing to attempt something slightly more difficult. Skill learning should be organised into a series of tasks that progress gradually and allow you to master each step before progressing on to the next. Personal success breeds confidence, while repeated personal failure diminishes it.
Being involved with the success of others can also significantly bolster your confidence, especially if you believe that the performer you are involved with (e.g. a team-mate) closely matches your own qualities or abilities. In effect, it evokes the reaction: “if they can do it, I can do it”.