The correct option is A does not acquaint him with the full potentialities of the new players.
In the given passage, it's written that early in the season when a reporter asks the coach about his new players, he does not reveal their abilities to their full extent to the reporter. Option A is correct because it's a contraction of the given sentence "a coach tends to talk down the abilities of his new man. He does not want his team to become known as a favourite ...", where "talk down" means "does not acquaint". Option B is incorrect because this is not the intent of the coach, he does not ridicule his rival teams, it's no where mentioned in the passage. Option C is incorrect because it's the opposite of what the coach actually does, he does not highlight the qualities, but hides them, as mentioned "tends to talk down the abilities". Option D is incorrect because the coach does not praise his team, but "talks down the abilities" of his team, where 'talk down' means talks less about the full extent of their abilities.