You don’t have to be a team captain to do those things, though. My kid tripled turnout for her academic team, and was NOT a captain. She led her team to a high finish in their state tournament and a respectable showing at nationals, and was NOT a captain. You don’t need the title to be a leader. Of course if you have been a captain, put it on your application. I would say to be careful about using it for your essay topic for top colleges, though – captains are a dime a dozen, and they see a lot of cliche essays about how much a student learned and overcame in their sports experience. You do better at a top school going against the tide… for example, if the OP is female, I would say an essay on her experience in boxing has the potential to be a MUCH stronger essay than one on volleyball. Admissions officers like to have their interest piqued and to find genuine, unique, interesting students to admit. Stand out from the crowd if you can.