A captain was the leader of a sports team, usually chosen based on their skill and leadership abilities.
In 2351, Benjamin Sisko was the captain of the Academy wrestling team at Starfleet Academy. (DS9: "Apocalypse Rising")
In 2353, Worf was the captain of his school soccer team on Gault. (DS9: "Let He Who Is Without Sin...")
Julian Bashir was the captain of the racquetball team at Starfleet Medical Academy. (DS9: "Rivals")
Harry Kim was the captain of the Velocity team. It was one of the accomplishments he included in his 2375 lament to Derran Tal about his discomfort with breaking rules. (VOY: "The Disease")
Also that year, to distract Ryan, a guard at Vic's lounge while it was under the management of Frankie Eyes, Kasidy Yates flirted with him, asking if he'd gone to high school in Asheville, North Carolina. When he denied having done so, she said he looked like the captain of the football team, who she had had a crush on. (DS9: "Badda-Bing, Badda-Bang")