This is the 17061st most frequent Russian word.
спортсмен
Athlete.
The word 'спортсмен' is used nominatively to describe the subject of the sentence, highlighting the individual's talent in sports.
Он талантливый спортсмен.
He is a talented athlete.
The word 'спортсмена' is in the accusative case because it is the direct object of the verb 'встретил'.
Вчера я встретил известного спортсмена на улице.
Yesterday, I met a famous athlete on the street.
In this sentence, the word 'спортсменом' is in the instrumental case, defining the means by which the admiration is expressed.