This is the 17406th most frequent Russian word.
теннисистов
Tennis players.
Here, 'теннисистов' is used in the accusative plural case as it is the direct object of the verb 'готовит', indicating whom the action is directed towards.
Тренер готовит теннисистов к важным соревнованиям.
The coach trains the tennis players for the important competition.
In this sentence, 'теннисистов' is in the genitive plural case, linked with the preposition 'за' to show possession or association.
Во время турнира судья внимательно следил за движениями теннисистов.
During the tournament, the referee closely observed the movements of the tennis players.
Here, 'теннисистов' is in the genitive plural case to indicate possession or relationship in the context of the rackets.