Why do people on sport teams get so competitive?

A lot of people get so competitive on sports teams because they like the feeling that they are better than another person on their own team or on another team. The feeling that they can do something better than another makes people feel confident and better about themselves. I've seen it on my team, one girl tries to swim better than another girl and that girl tries to swim better than a different girl. Its always competition. People don't want to look sloth-ish in front of coach, their friends or random strangers. I have also been really competitive with swimming. I want our team to do better than another or i want myself to be better than the girls on the team. Even though competitiveness does help people do better and succeed, it can also bring out the worst in people. i think its okay to be competitive, just not too competitive so that your frightening people or your working yourself too hard.