コーチは選手達が泳ぐのをじっと見ていた。

coach

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to swim

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

motionlessly (e.g. stand, wait); (be) still; fixedly (e.g. gaze, stare); intently (e.g. listen, think); patiently (endure); stoically; firmly (e.g. hold); restrained

to see; to look; to watch; to view; to observe; to look over; to look on; to assess; to examine; to judge; to look after; to keep an eye on; to take care of; to view (e.g. flowers, movie); to try; to try out; to see that...; to find that...