athlete 运动员
An athlete is a person who does any kind of physical sports, exercise, or games, especially in competitions. athlete是指参加任何形式的体育运动、锻炼或游戏的人，尤其是在比赛中。
例：
Mark Spitz was a great athlete.
马克·斯皮茨是一名伟大的运动员。
player 运动员；选手
A player in a sport or game is a person who takes part, either as a job or for fun.
Player是一项运动或游戏的参与者，是指为了工作或娱乐而参加的人。
例：
She was a good golfer and tennis player.
她曾是一名优秀的高尔夫球手和网球运动员。
英语母语人士点评：
Athlete is more professional, maybe someone who's full time job is sports.athlete更专业，也许他（她）的全职工作是运动。
Player can be anyone in any team.player可以是任何团队中的任何人。
Athlete also does not have to be in a team and can be someone who does sports like running regularly.
athlete也不一定需要在一个团队里。他（她）可以是从事某项运动的人，比如跑步。